List of Kamen Rider Build characters

Kamen Rider Build (仮面ライダービルド, Kamen Raidā Birudo) is a 2017 Japanese tokusatsu drama and the 28th entry in the Kamen Rider series. It is primarily set in Touto, an eastern region of Japan separated by the Skywall Disaster.

The main protagonists of the series: (from left to right) Ryūga Banjō (Eiji Akaso), Sento Kiryū (Atsuhiro Inukai), Kazumi Sawatari (Kouhei Takeda), and Gentoku Himuro (Kensei Mikami).

The protagonists in their Kamen Rider forms.

Nascita

Several characters gather at Nascita, a café owned by Sōichi Isurugi where he lives with his daughter Misora. They shelter Sento and later Ryuga. However, the revelation that Sōichi Isurugi is Blood Stalk, and had been possessed by the evil alien Evolto, compromises the café's status as a safehouse until he leaves Touto.

Sento Kiryu

Sento Kiryu (桐生 戦兎, Kiryū Sento) is a 26-year-old genius who is trustful and puts the safety of others above himself. Though level-headed and compassionate, Sento is egotistical with a dangerous temper when provoked.

Prior to the start of the series, he was found by Sōichi Isurugi with total amnesia except for being experimented upon by Night Rogue. Sōichi gave Sento his name and convinced him to help fight the Faust organization and its Smash creations in hope of regaining his memories. While helping Ryuga clear his name, Sento learns that an Evolto-possessed Sōichi masterminded the events that ruined both his and Ryuga's lives, and a defeated Gentoku reveals Sento's true identity.

During the events of Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider, Sento and Ryuga encounter some Bugsters in their world, fighting despite seeing their attacks don't work, Sento decides to use Ex-Aid's powers, seeing which have an effect, Kaiser is suddenly attacked and steals the bottles Sento recovers while Ryuga is thrown into a machine which sends him to a parallel world where the Skywall does not exist. Afterward, Sento meets Parad, who demands the Ex-Aid Fullbottles, where Sōichi appears and explains about Kaiser's, Sento and Parad decide to learn more about their plans. In the end, Sento, along with Emu and the other main Kamen Riders, decides to end the Kaiser duo's plan.

Sento was actually Faust's founder, Takumi Katsuragi, whose memories were lost after a failed assassination attempt on Evolto. After being knocked unconscious by Evolto, his face was swapped with the recently murdered musician Tarō Satō (佐藤 太郎, Satō Tarō), to be experimented upon by Gentoku as part of Evolto's plan to complete Takumi's Rider Systems for the civil war Evolto causes. However, Sento joins forces with Kazumi and Gentoku to fight against Evolto. After a failed suicide attack on Evolto, Katsuragi's personality re-emerges and tries to take matters into his own hands. Eventually, Sento and Katsuragi came to terms with each other, allowing the former to regain control of his body while the latter acted as his spiritual adviser.

Following Evolto's destruction and apparent erasure from Earth, Sento learned their world was assimilated into the "Prime" Kamen Rider universe with the Skywall Disaster and subsequent deaths averted. This left Sento misplaced, seen as a complete stranger or mistaken for Tarō Satō. He later finds his own reality's Ryuga, who was in the same situation, and the two decide to start their lives anew. It is later revealed that many of the previous episodes' opening recaps are actually memoirs written by Sento which he intends to use as the basis of a television series he and Ryuga are collaborating on, subtly breaking the fourth wall. During the Build New World films, Sento is convinced that Kamen Riders are no longer needed before changing his mind after Killbus appears on Earth. He later enlists Takumi's help to develop a serum that would restore the memories and abilities of himself and his fellow Kamen Riders from their universe.

Sento is able to transform into Kamen Rider Build by using the Build Driver (ビルドドライバー, Birudo Doraibā) to combine two Fullbottles (フルボトル, Furubotoru). Depending on the combination of Fullbottles, one of which corresponds to a person or animal and one which corresponds to an object, he can access various forms. Certain combinations work better than others, with strong forms called a Best Match (ベストマッチ, Besuto Matchi), which can perform the Voltech Finish (ボルテックフィニッシュ, Borutekku Finisshu) finisher. Weaker forms called a Trial Form (トライアルフォーム, Toraiaru Fōmu) can perform the Voltech Attack (ボルテックアタック, Borutekku Atakku) finisher. The Best Match forms are inspired by Misora Isurugi's childhood drawings, according to Sōichi's past memories. By himself, Sento's initial Hazard Level is 3 (see Smash, below). The continuous use of the Hazard Trigger and Pandora Panel (later Genius Fullbottle) allows it to rise rapidly towards 7, allowing him to transform the Rabbit Fullbottle into a golden state.

Best Matches:

• His "True Best Match" and default Best Match is Rabbit Tank Form (ラビットタンクフォーム, Rabitto Tanku Fōmu), a.k.a. "The Armored Moonsault" (鋼のムーンサルト, Hagane no Mūnsaruto). This form is achieved by using the Rabbit (ラビット, Rabitto) Fullbottle, which equips the spring-like Rabbit Foot Shoes (ラビットフットシューズ, Rabitto Futto Shūzu) spring on his left leg for superhuman reflexes, and the Tank (タンク, Tanku) Fullbottle, which equips the tread-like Tank Roller Shoes (タンクローラーシューズ, Tanku Rōrā Shūzu) tread on his right leg for enhanced kicking. Build later uses the drink can-like Rabbit Tank Sparkling (ラビットタンクスパークリング, Rabitto Tanku Supākuringu) to assume an upgraded version of his default form called Rabbit Tank Sparkling Form (ラビットタンクスパークリングフォーム, Rabitto Tanku Supākuringu Fōmu), a.k.a. the "Bubbling and Bursting" (シュワッと弾ける, Shuwatto Hajikeru), which allows him to use all of his Best Match weapons. This form first appears in the movie Kamen Rider Heisei Generations Final.
• Gorilla Mond Form (ゴリラモンドフォーム, Goriramondo Fōmu), a.k.a. the "Shining Destroyer" (輝きのデストロイヤー, Kagayaki no Desutoroiyā), uses the Gorilla (ゴリラ, Gorira) Fullbottle, which equips the Muscle Glove (マッスルグローブ, Massuru Gurōbu) on his right arm for superhuman strength, and the Diamond (ダイヤモンド, Daiyamondo) Fullbottle, which equips the BLD Prism Glove (BLDプリズムグローブ, BLD Purizumu Gurōbu) on his left arm for increased durability. Sento initially used this form as Takumi in Kamen Rider Ex-Aid, as well as its film Kamen Rider Ex-Aid the Movie: True Ending.
• Hawk Gatling Form (ホークガトリングフォーム, Hōku Gatoringu Fōmu), a.k.a. the "Rampage of the Skies" (天空の暴れん坊, Tenkū no Abarenbō), uses the Taka (タカ, Hawk) Fullbottle, which equips the Celestial Wings (ソレスタルウィング, Soresutaru Wingu) on his back for flight capabilities, and the Gatling (ガトリング, Gatoringu) Fullbottle, which grant enhanced accuracy. In this Best Match or any Trial Form using either Fullbottle, Build is armed with the handgun-likeHawk Gatlinger (ホークガトリンガー, Hōku Gatoringā) which allows him to perform the Full Bullet (フルバレット, Furu Baretto) finisher.
• Ninnin Comic Form (ニンニンコミックフォーム, Ninnin Komikku Fōmu), a.k.a. the "Sneaky Entertainer" (忍びのエンターテイナー, Shinobi no Entāteinā), uses the Ninjya (ニンジャ, Ninja) Fullbottle, which equips the sash-like Onmitsu Scarf (オンミツスカーフ, Onmitsu Sukāfu) on his back for camouflage capabilities, and the Comic (コミック, Komikku) Fullbottle, which grants the ability to project illusory images. In this Best Match or any Trial Form using either Fullbottle, Build is armed with the katana-like 4Koma Ninpoutou (4コマ忍法刀, Yon Koma Ninpōtō, Four-frame Ninja Sword) which allows him to perform one of two finishers: Fire Jutsu (火遁の術, Katon no Jutsu, Art of Fire Releasing) or Wind Jutsu (風遁の術, Fūton no Jutsu, Art of Wind Releasing).
• Rocket Panda Form (ロケットパンダフォーム, Roketto Panda Fōmu), a.k.a. the "Flying Monotone" (ぶっ飛びモノトーン, Buttobi Monotōn), uses the Panda (パンダ) Fullbottle which equips the claw-like Giant Scratcher (ジャイアントスクラッチャー, Jaianto Sukuratchā) on his right arm, and the Rocket (ロケット, Roketto) Fullbottle, which equips the missile-like Cosmo Builder (コスモビルダー, Kosumo Birudā) on his left arm.
• Fire Hedgehog Form (ファイヤーヘッジホッグフォーム, Faiyā Hejjihoggu Fōmu), a.k.a. the "Rescue Kenzan" (レスキュー剣山, Resukyū Kenzan), uses the Harinezumi (ハリネズミ, Hedgehog) Fullbottle which equips the tekko-like Spine Knuckle (スパインナックル, Supain Nakkuru) on his right arm for enhanced punching, and the Shoubousha (消防車, Shōbōsha, Fire engine) Fullbottle, which equips the hose-like Multi Deluge Gun (マルチデリュージガン, Maruchi Deryūji Gan) on his left arm for spraying fire or water.
• Lion Cleaner Form (ライオンクリーナーフォーム, Raion Kurīnā Fōmu), a.k.a. the "Maned Cyclone" (たてがみサイクロン, Tategami Saikuron), uses the Lion (ライオン, Raion) which equips the Gold Lio Gauntlet (ゴルドライオガントレット, Gorudo Raio Gantoretto) on his right arm for releasing bursts of energy, and the Soujiki (掃除機, Sōjiki, Vacuum cleaner) Fullbottle which equips the vacuum-like Long Range Cleaner (ロングレンジクリーナー, Rongu Renji Kurīnā) on his left arm for absorbing and storing attacks in the canister-like Trash Converter (トラッシュコンバーター, Torasshu Konbātā) on his left shoulder. Outside its compatibility with the Build Driver, the Lion Fullbottle can also be loaded into the smartphone-like Build Phone (ビルドフォン, Birudo Fon) to transform into a motorcycle known as the Machine Builder (マシンビルダー, Mashin Birudā).
• Key Dragon Form (キードラゴンフォーム, Kī Doragon Fōmu), a.k.a. the "Sealed Fantasia" (封印のファンタジスタ, Fūin no Fantajisuta), uses the Dragon (ドラゴン, Doragon) which equips the spike-like Fang Blades (ファングオブレイド, Fanguo Bureido) on his right arm, and the Lock (ロック, Rokku) Fullbottle, which equips the battering ram-like Bind Master Key (バインドマスターキー, Baindo Masutā Kī) on his left arm. In this Best Match or any Trial Form using either Fullbottle, Build is armed with the Beat Closer. This form is rarely used due to the strain the Dragon Fullbottle places on Sento's body, that's why Ryuga uses it instead of him.
• Kaizoku Ressya Form (海賊レッシャーフォーム, Kaizoku Resshā Fōmu, Pirate Train Form), a.k.a. the "Punctual Rebel" (定刻の反逆者, Teikoku no Hangyakusha), uses the Kaizoku (海賊, Pirate) Fullbottle, which equips the cape-like Multi Sail Mantle (マルチセイルマント, Maruchi Seiru Manto) on his right shoulder for increased agility, and the Densya (電車, Densha, Train) Fullbottle, which equips the Train Gauntlet (トレインガントレット, Torein Gantoretto) on his left arm for increased speed. In this Best Match or any Trial Form using either Fullbottle, Build is armed with the bladed bow-like Kaizoku Hassyar (カイゾクハッシャー, Kaizoku Hasshā) which allows him to perform the Kaizoku Densya (海賊電車, Kaizoku Densha) finisher.
• Octopus Light Form (オクトパスライトフォーム, Okutopasu Raito Fōmu), a.k.a. the "Lightning Technician" (稲妻テクニシャン, Inazuma Tekunishan), uses the Octopus (オクトパス, Okutopasu) Fullbottle, which equips the tentacle-like Twist Lash Arm (ツイストラッシュアーム, Tsuisuto Rasshu Āmu) on his right shoulder for binding opponents, and the Light (ライト, Raito) Fullbottle to equips the circuit breaker-like Shade Breaker (シェードブレイカー, Shēdo Bureikā) on his left arm for emitting bright flashes.
• Phoenix Robo Form (フェニックスロボフォーム, Fenikkusu Robo Fōmu), a.k.a. the "Immortal Weapon" (不死身の兵器, Fujimi no Heiki), uses the Phoenix (フェニックス, Fenikkusu) Fullbottle which equips Flame Reviber (フレイムリヴァイバー, Fureimu Rivaibā) gauntlet and Empirial Wings (エンパイリアルウィング, Enpairiaru Wingu), and the Robot (ロボット, Robotto) Fullbottle that equips the mechanical arm Demolition One (デモリションワン, Demorishon Wan) for dismantling and crushing targets. It was introduced in Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider.
• Smapho Wolf Form (スマホウルフフォーム, Sumaho Urufu Fōmu), a.k.a. the "Connected Lone Wolf" (つながる一匹狼, Tsunagaru Ippiki Ōkami), uses the Wolf (ウルフ, Urufu) Fullbottle to equip the Wolfatal Claw (ウルフェイタルクロー, Urufeitaru Kurō), and the Smapho (スマホ, Sumaho, Smartphone) Fullbottle to equip the buckler-like Build Pad Shield (ビルドパッドシールド, Birudo Paddo Shīrudo) on the left arm.
• Rose Copter Form (ローズコプターフォーム, Rōzu Koputā Fōmu), a.k.a. the "Passionate Fan" (情熱の扇風機, Jōnetsu no Senpūki), uses the Rose (ローズ, Rōzu) Fullbottle which equips the Ibalash Arm (イバラッシュアーム, Ibarasshu Āmu) to manipulate vines or fire thorns, and the Helicopter (ヘリコプター, Herikoputā) Fullbottle that equips the Batrotor Blade (バトローターブレード, Batorōtā Burēdo) helicopter rotor for flight.
• Tora UFO Form (トラユーフォーフォーム, Tora Yūfō Fōmu), a.k.a. the "Unidentified Jungle Hunter" (未確認ジャングルハンター, Mikakunin Janguru Hantā), uses the Tora (トラ, Tiger) Fullbottle to increase speed and equip the BLD Tora Fight Glove (BLDトラファイトグローブ, Bī Eru Dī Tora Faito Gurōbu), and the UFO (UFO, Yūfō) Fullbottle which allows Build to conjure a UFO projection to ride upon.
• Kujira Jet Form (クジラジェットフォーム, Kujira Jetto Fōmu), a.k.a. the "Sky-Flying Big Wave" (天駆けるビッグウェーブ, Amakakeru Biggu Wēbu), uses the Kujira (クジラ, Whale) Fullbottle which equips the BLD Spout Glove (BLDスパウトグローブ, Bī Eru Dī Supauto Gurōbu) which manipulates water currents, and the Jet (ジェット, Jetto) Fullbottle which equips the Aces Wings (エイセスウィング, Eisesu Wingu)[1] for flight and creates mini-jets from the Scramble Chest Armor (スクランブルチェストアーマー, Sukuranburu Chesuto Āmā)[1] to attack.
• Kirin Cyclone Form (キリンサイクロンフォーム, Kirin Saikuron Fōmu), a.k.a. the "Towering Storm-Caller" (嵐を呼ぶ巨塔, Arashi o Yobu Kyotō), uses the Kirin (キリン, Giraffe) Fullbottle which equips the horn-like Kirin Neckbreaker (キリンネックブリーカー, Kirin Nekkuburīkā)[1] on the right arm, and the Senpuki (扇風機, Senpūki, Fan) Fullbottle which equips the Cycstormer (サイクストーマー, Saikusutōmā)[1] on the left arm to create tornados.
• Turtle Watch Form (タートルウォッチフォーム, Tātoru Wotchi Fōmu), a.k.a. the "Armored Time Hopper" (時を駆ける甲冑, Toki o Kakeru Katchū), uses the Turtle (タートル, Tātoru) Fullbottle and the Watch (ウォッチ, Wotchi) Fullbottle. This form first appears in Kamen Rider Build episode 21 off-screen.

Build's main weapon is the Drill Crusher (ドリルクラッシャー, Doriru Kurasshā), which can operate as either a sword or a gun. By inserting a Fullbottle into a slot on the back of this weapon, it can perform the Voltech Break (ボルテックブレイク, Borutekku Bureiku) finisher. After defeating a Smash, Build can extract its element liquid into an Empty Bottle (エンプティボトル, Enputi Botoru) to be purified into a new Fullbottle to access a form or charge a weapon.

Sento later acquires a turbocharger-like item called the Hazard Trigger (ハザードトリガー, Hazādo Torigā), which allows him to transform into a black-colored version of Build called Hazard Form (ハザードフォーム, Hazādo Fōmu) whose upgraded Super Best Match (スーパーベストマッチ, Sūpā Besuto Matchi) forms are both stronger than RabbitTank Sparkling Form and equal to the Sclash Driver-using Kamen Riders. This form has two finishers: Overflow (オーバーフロー, Ōbāfurō) and Hazard Finish (ハザードフィニッシュ, Hazādo Finisshu). However, the Hazard Trigger induces a berserker side-effect, leading to a self-destruct mechanism being added to avoid a deadly rampage. After Misora awakens her full ability of purifying the Hazard Levels of Nebula Gas, she effectively negates the Hazard Trigger's side-effects.

Other Forms:

• The Fully Shook Rabbit Tank Bottle (フルフルラビットタンクボトル, Furu Furu Rabitto Tanku Botoru) is a special 2-in-1 Fullbottle device that can switch between the full forms of the Rabbit and Tank Fullbottles, granting access to the full potential of both. It also negates the side-effects of the Hazard Trigger. The Fully Shook Rabbit Tank Bottle's main weapon is the Fullbottle Buster (フルボトルバスター, Furubotoru Basutā), which has a sword-like Buster Blade Mode (バスターブレードモード, Basutā Burēdo Mōdo) and a shotgun-like Buster Cannon Mode (バスターキャノンモード, Basutā Kyanon Mōdo). By inserting up to four Fullbottles into the side of this weapon's barrel, it can activate several finishers.
  • Rabbit Rabbit Form (ラビットラビットフォーム, Rabitto Rabitto Fōmu), a.k.a. "A Crimson Speedy Jumper" (紅のスピーディージャンパー, Kurenai no Supīdī Janpā), is Build's speed form whose finisher is the Hazard Finish: Rabbit Rabbit Finish (ハザードフィニッシュ ラビットラビットフィニッシュ, Hazādo Finisshu Rabitto Rabitto Finisshu).
  • Tank Tank Form (タンクタンクフォーム, Tanku Tanku Fōmu), a.k.a. the "Blue Warrior of Steel" (鋼鉄のブルーウォーリア, Kōtetsu no Burū Wōria), is Build's strength form whose finisher is the Hazard Finish: Tank Tank Finish (ハザードフィニッシュ タンクタンクフィニッシュ, Hazādo Finisshu Tanku Tanku Finisshu).
• The Genius (ジーニアス, Jīniasu) Fullbottle was created by Takumi from a green Pandora Panel that combines the power of all 60 Fullbottles, enabling Build to access his ultimate form, Genius Form (ジーニアスフォーム, Jīniasu Fōmu), a.k.a. the "Completely Flawless Bottle Guy" (完全無欠のボトルヤロー, Kanzen Muketsu no Botoru Yarō). This form gives Build the ability to perform Hazard purification and fight toe-to-toe with Evol Black Hole Form via high-speed movement. He is also able to use the Fullbottle Buster while in this form. If attached with the Hazard Trigger, Build gains the ability to negate the Pandora Panel's effects on the Lost Fullbottles. This form has three finishers: Genius Attack (ジーニアスアタック, Jīniasu Attaku), Genius Break (ジーニアスブレイク, Jīniasu Bureiku), and Genius Finish (ジーニアスフィニッシュ, Jīniasu Finisshu). After the completion of the Pandora Box, Sento loses this form as the Genius Fullbottle returned to its original state. Although it is revealed in Build New World: Kamen Rider Cross-Z that Sento created a new Genius Fullbottle, and in Build New World: Kamen Rider Grease he resumes using this form.
• Rabbit Dragon Form (ラビットドラゴンフォーム, Rabitto Doragon Fōmu) is a special Best Match developed from samples of Build's Rabbit and Cross-Z's Dragon Fullbottles to create the Gold Rabbit (ゴールドラビット, Gōrudo Rabitto) and Silver Dragon (シルバードラゴン, Shirubā Doragon) Fullbottles by the events of Kamen Rider Build the Movie: Be the One for the purpose of destroying Evolto. As a Trial Form, this form's finisher is the Voltech Attack but it has a late Best Match announcement on the Build Driver due to Sento's resolve.
• Cross-Z Build Form (クローズビルドフォーム, Kurōzu Birudo Fōmu) is an enhanced form of Build's Rabbit Dragon Form that appears in Be The One, using the Cross-Z Build Can (クローズビルド缶, Kurōzu Birudo Kan) that Vernage created by temporarily fusing the Genius Bottle with the Gold Rabbit and Silver Dragon Fullbottles. Sento assumes the form while absorbing Ryūga during their fight against Kamen Rider Blood, like Kamen Rider Double, both Sento and Ryuga gain control in this form. After defeating the Blood Tribe, the Cross-Z Build Can separated back into three components. His finisher is the Love and Peace Finish (ラブ&ピースフィニッシュ, Robu Ando Pīsu Finisshu).

Best Matches in other media:

• Kuma Televi Form (クマテレビフォーム, Kuma Terebi Fōmu), a.k.a. the "Honey High Vision" (はちみつハイビジョン, Hachimitsu Hai Bijon), is accessed via the Kuma (クマ, Bear) and Televi (テレビ, Terebi, Television) Fullbottles. In this form, Build is armed with a giant claw that allows him to generate honey, and gains assistance in the form of an artificial intelligence Televi-san (てれびさん, Terebi-san). This form is exclusive to Kamen Rider Build: Birth! KumaTelevi!! Vs. Kamen Rider Grease.
• Same Bike Form (サメバイクフォーム, Same Baiku Fōmu), a.k.a. the "Solo-Running Hunter" (独走ハンター, Dokusō Hantā), is accessed via the Same (サメ, Shark) and Bike (バイク, Baiku) Fullbottles. It provides Build with echolocation to detect even invisible opponents and invoke energy constructs of Machine Builder. This form is exclusive to Kamen Rider Build: Raising the Hazard Level With 7 Best Matches.
• Exclusive to Kamen Rider Battle: Ganbarizing video game:
  • Beetle Camera Form (ビートルカメラフォーム, Bītoru Kamera Fōmu), a.k.a. the "Scoop King of the Forest" (密林のスクープキング, Mitsurin no Sukūpu Kingu), is accessed via the Kabutomushi (カブトムシ, Rhinoceros beetle) and Camera (カメラ, Kamera) Fullbottles.
  • Dog Mic Form (ドッグマイクフォーム, Doggu Maiku Fōmu), a.k.a. the "Big Sound of Healing" (癒しの大爆音, Iyashi no Daibakuon), is accessed via the Dog (ドッグ, Doggu) and Mic (マイク, Maiku) Fullbottles.
  • Merry Christmas Form (メリークリスマスフォーム, Merī Kurisumasu Fōmu), a.k.a. the "Holy Emissary" (聖なる使者, Seinaru Shisha), is accessed via the Santa Claus (サンタクロース, Santa Kurōsu) and Cake (ケーキ, Kēki) Fullbottles.
  • Uni Raser Form (ユニレイサーフォーム, Yuni Reisā Fōmu), a.k.a. the "One-Horned Erasure" (一角消去, Ikkaku Shōkyo), is accessed via the Unicorn (ユニコーン, Yunikōn) and Keshigomu (消しゴム, Keshigomu, Eraser) Fullbottles.
  • Shika Mid Form (シカミッドフォーム, Shika Middo Fōmu), a.k.a. the "Royal Family Guardian" (王家の守り神, Ōke no Mamorigami), is accessed via the Shika (シカ, Deer) and Pyramid (ピラミッド, Piramiddo) Fullbottles.
  • Penguin Skater Form (ペンギンスケーターフォーム, Pengin Sukētā Fōmu), a.k.a. the "Ice Sliding Peformer" (氷のスベり芸, Kōri no Suberi-gei), is accessed via the Penguin (ペンギン, Pengin) and Sukebo (スケボー, Sukebō, Skateboard) Fullbottles.
  • Mag Ghost Form (マグゴーストフォーム, Magu Gōsuto Fōmu), a.k.a. the "Wandering Attraction" (彷徨える超引力, Samayoeru Chōinryoku), is accessed via the Obake (おばけ, Ghost) and Magnet (マグネット, Magunetto) Fullbottles.
• Exclusive to the toyline:
  • Spider Cooler Form (スパイダークーラーフォーム, Supaidā Kūrā Fōmu), a.k.a. the "Cooling Trap Master" (冷却のトラップマスター, Reikyaku no Torappu Masutā), is accessed via the Spider (スパイダー, Supaidā) and Reizouko (冷蔵庫, Reizōko, Refrigerator) Fullbottles.
  • Bat Engine Form (バットエンジンフォーム, Batto Enjin Fōmu), a.k.a. the "Dark Mobility King" (暗黒の機動王 Ankoku no Kidōō), is accessed via the Bat (バット, Batto) and Engine (エンジン, Enjin) Fullbottles.
  • Hachi Marine Form (ハチマリンフォーム, Hachi Marin Fōmu), a.k.a. the "Deep Sea Worker" (深海の仕事人, Shinkai no Shigotonin), is accessed via the Hachi (ハチ, Wasp) and Sensuikan (潜水艦, Submarine) Fullbottles.
  • Sai Dryer Form (サイドライヤーフォーム, Sai Doraiyā Fōmu), a.k.a. the "Super Heating Continent" (超熱大陸, Chō Netsu Tairiku), is accessed via the Sai (サイ, Rhinoceros) and Dryer (ドライヤー, Doraiyā) Fullbottles.
• Legend Rider Best Match forms: Much like Kamen Rider Decade before him, Build can shapeshift into the primary forms of any of the previous lead Kamen Riders via Best Match function between two corresponding Fullbottles based on the previous lead Riders' motifs. In the Ganbarizing video game, if Build uses different Legend Rider Fullbottles for Trial Forms, Build will not shapeshift into the previous lead Kamen Riders. Most Legend Rider-themed Fullbottles have a compatible Best Match with one of Build's regular Fullbottles.
  • Ex-Aid Form (エグゼイドフォーム, Eguzeido Fōmu): Using the Doctor (ドクター, Dokutā) and Game (ゲーム, Gēmu) Fullbottles, Build shapeshifts into Kamen Rider Ex-Aid Action Gamer Level 2 where he is armed with the Gashacon Breaker. When purified, the Ex-Aid (エグゼイド, Eguzeido) Fullbottle splits into the two Fullbottles. This form is exclusive to Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider.
  • Exclusive to Ganbarizing video game:
    • Ghost Form (ゴーストフォーム, Gōsuto Fōmu): Using the Obake and Parka (パーカー, Pākā) Fullbottles, Build shapeshifts into Kamen Rider Ghost Ore Damashii where he is armed with the Gan Gun Saber.
    • Gaim Form (鎧武フォーム, Gaimu Fōmu): Using the Orange (オレンジ, Orenji) and Lock Fullbottles, Build shapeshifts into Kamen Rider Gaim Orange Arms where he is armed with the Daidamaru and Musou Saber.
    • Wizard Form (ウィザードフォーム, Wizādo Fōmu): Using the Mahoutsukai (魔法使い, Mahōtsukai, Magician) and Diamond Fullbottles, Build shapeshifts into Kamen Rider Wizard Flame Style where he is armed with the Wizarswordgun.
    • Fourze Form (フォーゼフォーム, Fōze Fōmu): Using the Yujou (友情, Yūjō, Friendship) and Rocket Fullbottles, Build shapeshifts into Kamen Rider Fourze Base States where he can manifest an Astroswitch's Fourze Module onto his limbs.
    • OOO Form (オーズフォーム, Ōzu Fōmu): Using the Taka and Medal (メダル, Medaru) Fullbottles, Build shapeshifts into Kamen Rider OOO Tatoba Combo where he is armed with the Medajalibur and Medagabryu.
    • Double Form (Wフォーム, Daburu Fōmu): Using the Tantei (探偵, Detective) and USB Memory (USBメモリ, Yū Esu Bī Memori) Fullbottles, Build shapeshifts into Kamen Rider Double CycloneJoker.
    • Decade Form (ディケイドフォーム, Dikeido Fōmu): Using the Card (カード, Kādo) and Camera Fullbottles, Build shapeshifts into Kamen Rider Decade where he is armed with the Ride Booker.
    • Den-O Form (電王フォーム, Den'ō Fōmu): Using the Momotaros (モモタロス, Momotarosu) and Densya Fullbottles, Build shapeshifts into Kamen Rider Den-O Sword Form where he is armed with the DenGasher.

Sento Kiryu is portrayed by Atsuhiro Inukai (犬飼 貴丈, Inukai Atsuhiro), who also portrays Tarō Satō.

Ryuga Banjo

Ryuga Banjo (万丈 龍我, Banjō Ryūga) is a 23-year-old former professional fighter who was born in Yokohama. Prior to his birth, a portion of Evolto's essence, which had come to Earth via a Martian probe, fused with the unborn Ryuga in a failed attempt to possess his mother Yuri Banjo (万丈 優里, Banjō Yuri) at the probe exhibit. As a result, Ryuga was born after only two months of gestation, and spent much of his childhood being tested by Namba Industries. Ryuga was orphaned at age 13 when his parents died in a traffic accident, and it was revealed in Build New World: Kamen Rider Cross-Z that Evolto actually murdered them to raise their son's Hazard Level. Takumi Katsuragi, the founder of Faust, learned of Ryuga's nature and hired him under false pretenses, intending to kill both Sōichi Isurugi into Ryuga while they were possessed by Evolto. Takumi's plan backfires, and Ryuga is framed for Takumi's apparent death. Ryuga was kidnapped from prison by Faust's agent Nabeshima for experimentation. Due to his half-alien physiology, Ryuga manages to escape and is found by Sento who hopes to learn of his past. Shortly after, Ryuga is forced to watch his girlfriend Kasumi Ogura be turned into a Smash, dying due to her low Hazard Level. Sento gave him the Dragon Fullbottle containing her Smash essence as a keepsake, and later a small robotic dragon-like companion known as the Cross-Z Dragon (クローズドラゴン, Kurōzu Doragon).

Ryuga is given a copy of the Build Driver from Sento, and adopted the mantle of Kamen Rider Cross-Z (仮面ライダークローズ, Kamen Raidā Kurōzu). During the events of Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider, Ryuga and Sento encounter some Bugsters in their world, after that Sento is attacked and Ryuga continues to be transported by him in parallel world where the Skywall does not exist, where he meets Emu and his friends, along with Emu decides to find out the plans of Reverse Kaiser, and thus put an end to the plans of the Kaisers.

Ryuga learned of his true origins from Vernage while manipulated by Evolto's machinations to strengthen his alien genes to make him a more-suitable host. During the events of the film Be the One, manipulated by Kengo Inō to attack Sento, Ryuga played a role in Sento's ability to assume Cross-Z Build Form when they absorbed him to defeat Kamen Rider Blood.

In the final clash against Evolto, Ryuga sacrifices himself to restrain a weakened Evolto as they are sucked into a wormhole created by the complete Pandora Box, with Evolto absorbing him in a final attempt to survive. Sento frees Ryuga as the alien is permanently destroyed. Due to Sento's actions, the Pandora Box transports Ryuga into the "Prime" Kamen Rider universe after it absorbed his reality. Sento finds him after running into the prime universe's Ryuga, an active sports fighter in a relationship with his reality's Kasumi. Ryuga then joins Sento in making a new life for themselves. In Build New World: Kamen Rider Cross-Z, Ryuga lives with Sento and makes a living selling Sento's experiments, until he meets Yui Mabuchi and joins forces with Evolto to defeat Killbus, starting a new relationship with Yui in the process. In Build New World: Kamen Rider Grease, he is in charge of delivering the Perfect Kingdom to Kazumi once Sento finishes creating it, so that he can defeat Keiji once and for all, in addition to saving Misora.

Due to Ryuga's alien origins and the experiments done on him by Faust, he has extraordinary abilities such as increased strength, being able to raise his Hazard Level faster than usual and manipulating the Pandora Box. Once reaching Hazard Level 7, Ryuga transformed the Dragon Fullbottle into the Silver Dragon Fullbottle. Although a strong fighter, Ryuga is easily provoked and not too intelligent. However, he was kind-hearted and generally puts others before himself. During Evolto's awakening of Phase 4, Cross-Z suffers from uncontrollable rage of his past life as Evolto, which also granted him the power of manipulating black holes at a smaller rate before they were ultimately neutralized when Vernage's essence was transferred into him during Misora's rescue.

The original Kamen Rider Cross-Z transforms by inserting the Dragon Fullbottle into the Cross-Z Dragon, which is then inserted into the Build Driver. Aside from gaining symmetrical Halfbodies, Cross-Z obtains the Drago Live Razor (ドラゴライブレイザー, Dorago Raibu Reizā) torso armor that allows him to channel Cross-Z Dragon Blaze (クローズドラゴン・ブレイズ, Kurōzu Doragon Bureizu) energy flames as attacks and empower his Dragonic Finish (ドラゴニックフィニッシュ, Doragonikku Finisshu) finisher. Unlike Build, Cross-Z can use the Dragon Fullbottle's powers due to the Cross-Z Dragon negating its side-effects. His main weapon is the sword-like Beat Closer (ビートクローザー, Bīto Kurōzā), which like the Drill Crusher can hold a Fullbottle for Cross-Z to perform one of three Special Tune (スペシャルチューン, Supesharu Chūn) finishers: Smash Slash (スマッシュスラッシュ, Sumasshu Surasshu), Million Slash (ミリオンスラッシュ, Mirion Surasshu), or Mega Slash (メガスラッシュ, Mega Surasshu). Said weapon is usually empowered by his Lock Fullbottle.

Additional forms:

• Kamen Rider Cross-Z Charge (仮面ライダークローズチャージ, Kamen Raidā Kurōzu Chāji) is Cross-Z's super form and a silver-colored upgrade that was accessed via the finalized Sclash Driver (スクラッシュドライバー, Sukurasshu Doraibā) and a Dragon Sclashjelly (スクラッシュゼリー, Sukurasshu Zerī). Sento was meant to use it at the height of Hokuto's invasion on Touto, but was forced to relinquish it to Ryuga for his higher Hazard Level. His finisher is the Scrap Break (スクラップブレイク, Sukurappu Bureiku). Cross-Z Charge's main weapon is the Twin Breaker (ツインブレイカー, Tsuin Bureikā), which has a gun-like Beam Mode (ビームモード, Bīmu Mōdo) and a jackhammer-like Attack Mode (アタックモード, Attaku Mōdo). Unlike the Drill Crusher and Beat Closer, the Twin Breaker can hold up to two Fullbottles and Sclashjellies, and either the Rabbit Tank Sparkling or the Cross-Z Dragon, for him to perform its finisher. Inserting an organic Fullbottle into the Sclash Driver allows Cross-Z Charge to perform the Charge Crash (チャージクラッシュ, Chāji Kurasshu), having once used the Taka Fullbottle for flight purposes. However, usage of the Sclash Driver exposes Ryūga to unfiltered Nebula Gas which causes him to become aggressive until he is later able to overcome this effect. This form was lost when Ryūga shielded Vernage at the cost of his Dragon Sclashjelly. Although another Dragon Sclashjelly was created, he lent it to Grease as Cross-Z favors his later upgrades instead. Ryuga uses this form again in Kamen Rider Heisei Generations FOREVER and in Build New World: Kamen Rider Cross-Z.
• Kamen Rider Cross-Z Magma (仮面ライダークローズマグマ, Kamen Raidā Kurōzu Maguma), a.k.a. the "Extreme Heat Muscle" (極熱筋肉, Gokunetsu Kinniku), is Cross-Z's initial final form, accessed by inserting the Cross-Z Magma Knuckle (クローズマグマナックル, Kurōzu Maguma Nakkuru) loaded with the Dragon Magma (ドラゴンマグマ, Doragon Maguma) Fullbottle into the Build Driver. Although its purpose as an upgraded form was envisioned, further developments were put on hold as the three Riders tried to storm the Pandora Tower until Ryūga's own resolve completed the Dragon Magma Fullbottle as the final component. By himself, Cross-Z Magma can channel Variable Magma (ヴァリアブルマグマ, Variaburu Maguma) as empowerment for attacks, creating snake-dragon constructs and manifesting a pair of wings for flight. His finisher in this form is the Volcanic Finish (ボルケニックフィニッシュ, Borukenikku Finisshu). With the Cross-Z Magma Knuckle as a handheld weapon, he can perform the Volcanic Knuckle (ボルケニックナックル, Borukenikku Nakkuru) finisher by channeling the power of any Fullbottles it used. Before relinquishing it to Grease, Cross-Z Magma was briefly in possession of the incomplete Blizzard Knuckle (ブリザードナックル, Burizādo Nakkuru), having aided in its creation. With the Silver Dragon Fullbottle, he can perform Glacial Knuckle (グレイシャルナックル, Gureisharu Nakkuru) finisher and weaken Evolto's DNA. In the final battle on Pandora Tower, use the Hazard Trigger, which allows him to fight on par with Evol Black Hole Form before the latter's transition into his monster form.
• Kamen Rider Great Cross-Z (仮面ライダーグレートクローズ, Kamen Raidā Gurēto Kurōzu) is an upgraded variant of the original Cross-Z, accessed by inserting the Great Cross-Z Dragon (グレートクローズドラゴン, Gurēto Kurōzu Doragon) loaded with the Great Dragon (グレートドラゴン, Gurēto Doragon) Evol-Bottle into the Build Driver. Having lost Evolto's genes on his body after his liberation from possession, Ryūga regains it by stealing the Dragon Evol-Bottle as it upgraded into its current form. His finisher in this form is the Great Dragonic Finish (グレートドラゴニックフィニッシュ, Gurēto Doragonikku Finisshu).
• Kamen Rider Cross-Z Evol (仮面ライダークローズエボル, Kamen Raidā Kurōzu Eboru), a.k.a. "The Invincible Galaxy Muscle Guy" (銀河無敵の筋肉野郎, Ginga Muteki no Kinniku Yarō), is Cross-Z's true final form accessed by using the Muscle Galaxy (マッスルギャラクシー, Massuru Gyarakushī) Fullbottle in the Build Driver. It combines the power of Cross-Z and Evol, in addition, Ryuga absorbs Evol by using this form, invoking Evol's Black Hole Form, unlike Cross-Z Build, Ryuga is the one who takes control in this form for as long as Evolto gives him power. This form has three finishers: Muscle Finish (マッスルフィニッシュ, Massuru Finisshu), Galaxy Finish (ギャラクシーフィニッシュ, Gyarakushī Finisshu), Muscle Galaxy Finish (マッスルギャラクシーフィニッシュ, Massuru Gyarakushī Finisshu). This form is exclusive to Build New World: Kamen Rider Cross-Z.

Ryuga Banjo is portrayed by Eiji Akaso (赤楚 衛二, Akaso Eiji).

Misora Isurugi

Misora Isurugi (石動 美空, Isurugi Misora) is Sōichi's 19-year-old daughter who works as Sento's assistant. She gained supernatural power after being exposed to the Pandora Box and spending seven years in a coma. She played a role in Project Build, as Evolto used Sōichi's memories of her drawings of organic and inorganic-based objects to influence Shinobu in developing the Best Match aspect of the technology. She was kidnapped by Faust for experimentation until Sōichi rescued her a year ago. Fearing that Faust is still hunting her, she remained in Nascita while using her online idol identity Miitan (みーたん, Mītan) to gather Smash intel and occasionally money from her fanbase. Misora was unaware that her father is actually a high-ranking Faust agent who used her, Sento and Ryuga as tools to create a Kamen Rider army within Touto, though she may have learned of this while being driven to despair. She later uses her powers to cure Taizan Himuro of Sōichi's poison so he can resume his duties as Touto's prime minister and thereafter discovers that her father is possessed by Evolto, the true villain committing the crimes.

During the events of Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider, Misora is in charge of purifying the Ex-Aid bottle in two, she also helps Sento find out Kaiser's hiding place.

Misora possesses the ability to purify and enhance Nebula Gas which made her a target of Faust. Initially, using the ability put her to sleep for a week; Sento later developed a machine to mitigate this. After she is nearly killed by a berserk Build Hazard Form, her ability increases so she can purify the higher Nebula Gas concentrations like those from the Hazard Trigger. Sento used her power to create the Fully Shook Rabbit Tank Bottle and Fullbottle Buster to negate the Hazard Trigger's side-effects. During the invasion by Seito, the western part of Japan, Misora's Martian bracelet is revealed to house the spirit of the Martian Vernage and the source of Misora's power. Misora was later kidnapped by Evolto and turned into the CD Lost Smash (CDロストスマッシュ, Shī Dī Rosuto Sumasshu) that can throw Glare Slicer (グレアスライサー, Gurea Suraisā) discs. Sento saves her by extracting Vernage to render Misora completely human and transfers the alien into Ryuga.

After the universes are merged at the conclusion of the series, an alternate Misora is shown to be a waitress at her father's café. In Build New World: Kamen Rider Cross-Z she recovers the memories of her alternate self after Killbus began the process of destruction with the Pandora Box. In Build New World: Kamen Rider Grease she runs Piccolo Nascita, a mobile café. After Downfall is defeated, she dates Kazumi.

Misora Isurugi is portrayed by Kaho Takada (高田 夏帆, Takada Kaho). As a child, Misora is portrayed by Noel Moriyama (森山 のえる, Moriyama Noeru).

Sawa Takigawa

Sawa Takigawa (滝川 紗羽, Takigawa Sawa) is a 27-year-old freelance journalist dedicated to learning about Build and the Smash. Build saved her from the Needle Smash, and she assists Sento after learning his true identity. While she is a spy for Namba Heavy Industries, Sawa is actually using her position to investigate the cover-up of an industrial accident she believes killed her father. When Misora exposed her duplicity, Sawa is punished by being turned into the octopus-themed Stretch Smash (ストレッチスマッシュ, Sutoretchi Sumasshu) before she is defeated by Ryuga with Sento extracting the Nebula Gas from her system. She then decides to atone for her actions and join forces with Sento's group to fight against Namba and Faust. Sawa becomes protective of Misora, especially after learning of the younger woman's past.

During the events of Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider, Sawa helps Sento find out about Kaiser's past.

Sawa is later revealed to be a brainwashed Namba agent, her motivating drive about her father being a fabrication. She was supposed to let herself die after failing Namba's mission but the familial bonds she made with Sento and the others gave her a reason to live and influenced her decision to cut ties with Namba. Sawa accomplishes this by aiding Sento in the ploy to trick Namba by giving him a fragment of Sento's research on the Fully Shook Rabbit Tank Bottle; Kazumi rescues the Nabeshima family whom Namba held hostage as leverage against Sawa, freeing her from Namba's control. She later helps take care of Sōichi, who had entered a coma after Evolto releases him from his control.

After Sento merged his world with that of the "Prime" Kamen Rider universe, an alternate Sawa is shown to also be working as a journalist. She nervously passed a business card to this new world's version of Gentoku for an interview. In Build New World: Kamen Rider Cross-Z she recovers the memories of her alternate self after Killbus began the process of destruction with the Pandora Box. In Build New World: Kamen Rider Grease she reveals to Sento and Ryūga that she is dating Gentoku.

Sawa Takigawa is portrayed by Yukari Taki (滝 裕可里, Taki Yukari).

Sōichi Isurugi

Sōichi Isurugi (石動 惣一, Isurugi Sōichi) is the enigmatic 48-year-old owner of Nascita and Misora's father who is actually Faust's high-ranking member Blood Stalk (ブラッドスターク, Buraddo Sutāku). He is a kind-hearted man and a good friend to Takumi's father Shinobu Katsuragi. Ten years prior to the series, he was the astronaut who discovered the abandoned Evol-Driver and the Pandora Box on Mars. This resulted in his possession by the alien entity Evolto who used him to commit numerous atrocities including the Skywall Disaster, framing Shinobu, and manipulating Takumi and Misora for his own ends. Sōichi's personality occasionally resurfaces to briefly fight Evolto before being suppressed. Sōichi was tricked into thinking that Evolto would leave his body upon retrieving the Evol-Driver, ending up in a coma; in the meantime Evolto possessed Ryūga then Sento before creating his own body in Sōichi's image.

After Sento merged his world with that of the "Prime" Kamen Rider universe, an alternate Sōichi is shown as an ordinary café-owner of Nascita, when Killbus restored the Pandora Box because Sōichi was never experienced with Nebula Gas, he was unable to recover his memories due to being possessed by Evolto.

Due to being possessed by Evolto, Sōichi gains several inhuman abilities. He can transmute matter, as shown when he transformed his tablet computer into pieces of paper. He can reshape a person's face and manipulate their memories. He can quickly leap into the air to escape.

When Evolto possessed him, Sōichi uses the Cobra (コブラ, Kobura) Fullbottle to transform into Blood Stalk. As Blood Stalk, he can poison his opponents by stabbing them with an appendage, and hack Touto's Guardians with a simple flick. Through his animal motif, he can summon a projection of a large cobra for various applications. With the Devil Steam, he is able to either release Nebula Gas to change regular people into Smash via the Steam Blade or inject a Smash with a Nebula Gas-filled bullet to enlarge them into giants via the Steam Rifle. Via Rocket Fullbottle, Stalk can launch guided energy missiles.

Sōichi Isurugi is portrayed by Yasuyuki Maekawa (前川 泰之, Maekawa Yasuyuki).

Sawatari Farm

Sawatari Farm (猿渡ファーム, Sawatari Fāmu) is the Sawatari family's potato farm in Hokuto, the northern region of Japan isolated by the Skywall Disaster. As the disaster made the region's soil infertile, Kazumi used his life's savings to support his workers. To continue doing so, he enlisted in the military, followed by a group of his farm workers who formed a unit called the Hokuto Three Crows. The remaining workers were all loyal to him, to the point of refusing his arrival when Namba Heavy Industries used them as hostages.

Kazumi Sawatari

Kazumi Sawatari (猿渡 一海, Sawatari Kazumi) is a 29-year-old soldier from Hokuto and the current owner of his farm. In hopes of obtaining more financial support, Kazumi volunteered for Hokuto's military and underwent Faust's human experimentation. Lying about his memory loss, Kazumi continued to use the Sclash Driver, which turned him into a bloodthirsty fighter, though he was able to control this effect. However, he despises cruelty; he threatened Hokuto's prime minister for ordering troops to target civilians during their invasion of Touto. He cares for his co-workers' welfare and was visibly upset when the Hokuto Three Crows underwent additional Nebula Gas infusion, knowing that their next defeat would guarantee their deaths. He is a fan of Misora, having watched her performances alongside his co-workers.

Having first infiltrated Touto during the events of Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider to reclaim the Phoenix and Robot Fullbottles for Hokuto, Kazumi is deployed to lead the Hokuto army to invade Touto. His alter-ego, Kamen Rider Grease (仮面ライダーグリス, Kamen Raidā Gurisu), was created based on the Robot Fullbottle. The invasion ends with Grease defeated by Build Hawk Gatling Hazard, and Cross-Z Charge saving Grease when Sento's Hazard Trigger goes berserk. During Seito's attack on Hokuto and Touto, he joins forces with those from Nascita in hopes of reclaiming his country. The Three Crows are killed and he gradually comes to terms with the loss, making peace with Sento and Gentoku. In hopes of catching up with Build and Cross-Z's growth in power, Kazumi and Gentoku allowed themselves to be kidnapped to forcefully raise their Hazard Levels at the risk of their lives.

Kazumi fought alongside the Touto Riders to stop Evolto's genocidal plans. During that time, Sento created the Blizzard Knuckle for Grease, but made it incompatible with Sclash Driver, which might have been fatal. When facing powerful replicas of the Three Crows which Evolto created as his enforcers, Kazumi uses the Blizzard Knuckle in Shinobu's Build Driver to destroy the copies at the cost of his life, dissipating in Misora's arms.

After Sento merged the worlds at the end of the series, an alternate Hokuto Three Crows try to set Kazumi on a blind date with Misora at Nascita. In Build New World: Kamen Rider Cross-Z he recovers the memories of his alternate self along with the power to transform into Grease after Killbus began the process of destruction with the Pandora Box, helping Ryuga in his fight against Killbus. In Build New World: Kamen Rider Grease, he and the Hokuto Three Crows are the only ones who did not lose their powers because they bathed in a special water that was left of the old world, which is why only Kazumi could defeat Keiji and Downfall and thus save Misora, which he accomplishes after becoming Grease Perfect Kingdom.

By himself, the injection of Nebula Gas allows Kazumi to utilize a Fullbottle's power at a smaller rate, which was enough to incinerate a Hazard Smash. He has the following forms:

• The original Kamen Rider Grease is transformed through the use of the Sclash Driver and Robot Sclashjelly, with his finisher being the Scrap Finish (スクラップックフィニッシュ, Sukurappu Finisshu). His main weapon is the Twin Breaker, which channels the power of either two Fullbottles or one mixed with his Robot Sclashjelly. By inserting an inorganic Fullbottle into the Sclash Driver, Grease can perform the Discharge Crash (ディスチャージクラッシュ, Disuchāji Kurasshu), manifesting Variable Jelly (ヴァリアブルゼリー, Variaburu Zerī) per various attacks or means of transportation. Before receiving his own upgraded form, Grease was provided another Dragon Sclashjelly, allowing him to use another copy of the Twin Breaker and therefore saving his life from disappearing as a result of his heightened Hazard Level.
• Kamen Rider Grease Blizzard (仮面ライダーグリスブリザード, Kamen Raidā Gurisu Burizādo), a.k.a. the "Frozen Soul Fire" (激凍心火, Gekitō Shinka), is Grease's super form accessed by inserting the Grease Blizzard Knuckle (グリスブリザードナックル, Gurisu Burizādo Nakkuru) loaded with the North Blizzard (ノースブリザード, Nōsu Burizādo) Fullbottle into the Build Driver that originally belonged to Shinobu. In this form, Grease Blizzard is armed with the GBZ Demolition One (GBZデモリションワン, Jī Bī Zetto Demorishon Wan) on his left arm and can generate Variable Ice (ヴァリアブルアイス, Variaburu Aisu) frozen liquid to empower his attacks. The GBZ Demolition One allows him to perform the Glacial Attack (グレイシャルアタック, Gureisharu Atakku), whereas his true finisher is the Glacial Finish (グレイシャルフィニッシュ, Gureisharu Finisshu). The Grease Blizzard Knuckle was created by Sento as a countermeasure for Evolto. Initially wielded by Cross-Z Magma, Kazumi was given the weapon with the North Blizzard Fullbottle. Kazumi returns using this form in Build New World: Kamen Rider Grease.
• Kamen Rider Grease Perfect Kingdom (グリスパーフェクトキングダム, Gurisu Pāfekuto Kingudamu), a.k.a. the Farmers Festival (ファーマーズフェスティバル, Fāmāzu Fesutibaru) is Grease's final form, this form is the fusion of the powers of Kazumi with the powers of the Hokuto Three Crows, this form is also accessed with the Build Driver. This form has two finishers: Stag Slash (スタッグスラッシュ, Staggu Surasshu) and Perfect Kingdom Finish (パーフェクトキングダムフィニッシュ, Pāfekuto Kingudamu Finisshu). Initially, it was believed that the Crows had sacrificed their lives to ensure the completion of this form, but it is later revealed that Sento completed the power-up item in time, preventing the Crows from dying when they sacrificed their powers. This form is exclusive to Build New World: Kamen Rider Grease.

Kazumi Sawatari is portrayed by Kouhei Takeda (武田 航平, Takeda Kōhei). The numbers on his character's dog tags are a play on the name of a character he previously portrayed in Kamen Rider Kiva, Otoya Kurenai.

Hokuto Three Crows

The Hokuto Three Crows (北都三羽ガラス, Hokuto Sanba Garasu) are a group of Hokuto soldiers who were originally workers of the Sawatari farm who enlisted to repay a debt to their former employer. Using Shinobu Katsuragi's Lost Fullbottles, they are each able to transform into enhanced form of the Smash known as Hard Smash (ハードスマッシュ, Hādo Sumasshu) and later the stronger Hazard Smash (ハザードスマッシュ, Hazādo Sumasshu), which gave increased strength but kills the user if they are knocked out of a transformation. Following their deaths, Grease kept their Bottles as memorabilia and had once combined their energies to perform a stronger attack. Evolto later creates corrupted copies of them to serve as his enforcers, but Kamen Rider Grease gave his life to destroy them. When Sento fuses the two worlds, an alternate Hokuto Three Crows are seen entering the cafeteria Nascita together with Kazumi. In Build New World: Kamen Rider Cross-Z, they recover the memories of their alternate selves along with the power to transform into Smash after Killbus began the process of destruction with the Pandora Box. During the events of Kamen Rider Build NEW WORLD: Kamen Rider Grease, they sacrificed their powers and seemingly their lives to ensure Grease can transform into his Perfect Kingdom Form, but are later revealed to have survived, pretending to have died in order to give Kazumi the push he needed to defeat Keiji Uraga.

Akaba

Akaba (赤羽), real name Masaru Ooyama (大山 勝, Ōyama Masaru), uses the Castle (キャッスル, Kyassuru) Fullbottle to transform into the Castle Hard Smash (キャッスルハードスマッシュ, Kyassuru Hādo Sumasshu) that has the Catapulta Cannon (カタプルタキャノン, Katapuruta Kyanon) on his head and the two Ground Rampart (グランドランパート, Gurando Ranpāto) shields on his shoulder pads. He seems to possess a violent streak when he attacks civilians without hesitation, but is ultimately loyal to Kazumi, following his decisions even when he questions them. When Seito invaded Touto to steal the Pandora Box, Akaba sacrificed his life to protect it from Gentoku, but ultimately failed to prevent the theft.

Akaba is portrayed by Eishin (栄信).

Aoba

Aoba (青羽), real name Syuuya Aikawa (相河 修也, Aikawa Shūya), uses the Kuwagata (クワガタ, Stag beetle) Fullbottle to transform into the stag beetle-themed Stag Hard Smash (スタッグハードスマッシュ, Sutaggu Hādo Sumasshu) that is armed with two sword-like Rapture Scissors (ラプチャーシザース, Rapuchā Shizāsu). Despite his looks and mannerisms, Aoba is one of the kinder members of the Three Crows. He is unexpectedly killed during battle when Build goes on a rampage and uses the Hazard Finish against him. Aoba's death shocked both his own comrades and the Touto Riders, especially Sento who became depressed for taking a life. Kazumi later forgives Sento.

Aoba is portrayed by Tateto Serizawa (芹澤 興人, Serizawa Tateto).

Kiba

Kiba (黄羽), real name Syoukichi Mihara (三原 聖吉, Mihara Shōkichi), uses the Fukurou (フクロウ, Fukurō, Owl) Fullbottle to transform into the Owl Hard Smash (オウルハードスマッシュ, Ōru Hādo Sumasshu) that has the two Forest Seeker (フォレストシーカー, Foresuto Shīkā) drones on his gauntlets. He behaves childishly, even acting literally like a child throwing a fit when defeated by Build in one battle. After Aoba's death, he becomes bitter and increasingly violent in combat. While trying to defend his homeland from Seito's invasion, Kiba becomes the Washio Brothers' hostage to force Kazumi into serving Seito. Despite Kazumi's effort to save him, Kiba is killed protecting Kazumi. His bottle is then used by a brainwashed Prime Minister Tajimi, until Build freed her from Nebula Gas exposure.

Kiba is portrayed by Takuya Yoshimura (吉村 卓也, Yoshimura Takuya).

Faust

Faust (ファウスト, Fausuto) is a mysterious terrorist organization that experiment on humans to create the Smash creatures. It was founded by Touto scientists Takumi Katsuragi and Gentoku Himuro. They are in possession of one of the Pandora Box's panels that was split during the Skywall Disaster, along with Nebula Gas they extracted from the Skywall and liquefied for the development of Fullbottles. According to Gentoku, Faust's objectives are to achieve Takumi's goals of evolving humanity into the "ultimate lifeform". The organization was compromised by Evolto and Namba who sought to reassemble the Pandora Box and repeat the calamity that destroyed the ancient Martian civilization.

Since forming in Touto, Faust members infiltrated the Touto Institute of Advanced Matter Physics (東都先端物質学研究所, Tōto Sentan Busshitsugaku Kenkyūjo), which had been studying the Pandora Box and protecting it from neighboring countries. Despite their pacifist ideals and public image as peacekeepers, Touto Institute was influenced by Faust to mass-produce weapons and use lethal force when pursuing convicts. During Gentoku's temporary takeover as the prime minister, Faust relocated from Touto and manipulated the two other nations into a war to acquire all of the Pandora Box panels and reassemble it to take over the Earth, when Evolto revealed his true plans. The organization then reorganized under Evolto's control.

Faust's leaders use the Transteam System (トランスチームシステム, Toransuchīmu Shisutemu), which Takumi Katsuragi reverse-engineered from Kaisei Mogami's Kaiser System. It requires organic Fullbottles to transform, with their identities concealed by built-in voice changers in their armor. Their main weapons are the Transteam Gun (トランスチームガン, Toransuchīmu Gan) which allows them to perform the Steam Break (スチームブレイク, Suchīmu Bureiku) and Steam Attack (スチームアタック, Suchīmu Atakku) finishers, and the Steam Blade (スチームブレード, Suchīmu Burēdo) which allows them to execute the Elek Steam (エレキスチーム, Ereki Suchīmu), Ice Steam (アイススチーム, Aisu Suchīmu) and Devil Steam (デビルスチーム, Debiru Suchīmu) attacks. Each of the leaders can also combine their weapons into the Steam Rifle (スチームライフル, Suchīmu Raifuru) to perform one of two finishers: Steam Shot (スチームショット, Suchīmu Shotto) or Steam Attack.

Gentoku Himuro

Gentoku Himuro (氷室 幻徳, Himuro Gentoku) is the 35-year-old special advisor to his father, Prime Minister Taizan Himuro, and head of the Touto Institute. Initially a kind, friendly and laid-back eccentric, radiation from the Skywall Disaster transformed him into a sadistic and paranoid power-hungry maniac, who performed questionable acts for Touto's safety after deeming his father's pacifism a liability. Gentoku orchestrated Takumi's expulsion from Touto Institute to cover for the Devil's Scientist while unknowingly being manipulated by Sōichi Isurugi (and by extension, Evolto and Namba). After taking his late friend's position as the prime minister's advisor, Gentoku took the mantle of Night Rogue and declared his leadership over Faust.

During the events of Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider, Gentoku helps Sento find out about Kaiser's past.

Gentoku took advantage of Sento and Ryuga to gather more Fullbottles, perfecting most of Takumi's Rider Systems and reclaiming the Pandora Box. Gentoku was elevated to prime minister after Stalk incapacitated his father and forced the two Kamen Riders to be inducted into Touto's military. After sending Cross-Z Charge to invade Hokuto, he was dismissed by Taizan and sentenced to exile. This forced him to seek refuge at Namba Heavy Industries and served Seito's military as Kamen Rider Rogue. The experiment Gentoku received to raise his Hazard Level rendered him a near-emotionless nihilist with a restraining chip to ensure obedience, while reversing the negative effects from the Skywall radiation. Although working under Namba, Gentoku secretly assisted the Riders. During an operation to rescue Taizan, Sento deactivated the restraining chip, allowing Gentoku to return at the cost of Evolto regaining his power as Kamen Rider Evol. After Taizan sacrifices himself to save Gentoku, Gentoku begins to seek redemption by allying himself with the Riders against Evolto and Namba, and begins to atone his past actions while reverting to his true personality.

Gentoku's initial Hazard Level is 3, raised to 4 by Namba Heavy Industries experimentation so that he can use the Sclash Driver. In hopes of matching the growth of Build and Cross-Z, both Kazumi and Gentoku allowed themselves to be captured and heavily dosed with Nebula Gas to further raise their Hazard Levels. As the battle against Evolto reaches the climax, Gentoku is distraught when Utsumi sacrifices himself and Kazumi falls in battle. He ultimately dies protecting the others during a clash with Evolto, successfully landing a critical blow on the alien.

When the universes are merged at the conclusion of the series, an alternate Gentoku is working as a personal aide to his father, with a shy but polite attitude towards his world's version of Sawa. In Build New World: Kamen Rider Cross-Z he recovers the memories of his alternate self and the power to transform into Rogue after Killbus began the process of destruction with the Pandora Box, helping Ryuga in his fight against Killbus. In Build New World: Kamen Rider Grease he tries to stop Downfall, but because his powers are stolen, he fails and is kidnapped but is later released thanks to Sawa after that Downfall is defeated, he tells Sento and Ryuga that he is dating Sawa.

Gentoku's forms are accessed through the Transteam system and/or Sclash Driver:

• Night Rogue (ナイトローグ, Naito Rōgu) is Gentoku's first transformation as the leader of Faust, accessed through the use of the Transteam Gun loaded with the Lost Fullbottle counterpart of the Bat Fullbottle. Aside from being a skilled combatant, he can manipulate steams from his body for quick travel and an electrical energy punch. Through his animal motif, he is capable of clinging to ceilings and creating a pair of bat wings, allowing him to swoop about at high speeds while performing powerful dive-bomb attacks. These items were relinquished to Utsumi once Gentoku became Kamen Rider Rogue.
• Kamen Rider Rogue (仮面ライダーローグ, Kamen Raidā Rōgu) is Gentoku's later alter-ego, accessed through the use of the Sclash Driver in conjunction with the Crocodile Crack (クロコダイルクラック, Kurokodairu Kurakku) Fullbottle. Having strength that rivals even Build's Hazard forms, he is armed with the Nebula Steam Gun. Using the Sclash Driver, Rogue can perform the Crack Up Finish (クラックアップフィニッシュ, Kurakku Appu Finisshu) finisher. Using the Nebula Steam Gun, he can perform one of two finishers; the Funky Break (ファンキーブレイク, Fankī Bureiku) in its Gun Mode or the Funky Shot (ファンキーショット, Fankī Shotto) in its Rifle Mode. As with the general function of both Sclash Drivers and Nebula Steam Gun, Gentoku can use the power of a single Fullbottle and auxiliary attacks.
• Kamen Rider Prime Rogue (仮面ライダーロープライムローグ, Kamen Raidā Puraimu Rōgu) is an upgraded form of Kamen Rider Rogue, accessed by using the Prime Rogue Fullbottle in the Build Driver. This form's finisher is the Prime Scrap Break (プライムスクラップブレイク, Puraimu Sukurappu Bureiku) and the Fullbottle breaks after its usage due to Gentoku's reckless usage, requiring a month be fixed. This form only appears in Kamen Rider Prime Rogue and Build New World: Kamen Rider Grease.

Gentoku Himuro is portrayed by Kensei Mikami (水上 剣星, Mikami Kensei).

Faust agents

Masahiro Nabeshima

Masahiro Nabeshima (鍋島 正弘, Nabeshima Masahiro) is a prison guard who frames Ryuga Banjo for the death of Touto Institute researcher Takumi Katsuragi, then delivers Ryūga to Faust for experimentation. After luring Sento and Ryuga to Seito, he was converted into Mirage Smash as a "reward" and later into Square Smash as part of Blood Stalk's experiment. Although rescued by Build and Ryuga, the experiments erased almost all of his memories. Sometime later, he regained his memories and revealed information about Faust to Sento, including Blood Stalk's identity. He and his family later are captured by Namba and used to force Sawa to betray her friends.

• Mirage Smash (ミラージュスマッシュ, Mirāju Sumasshu): Nabeshima's swordsman/ninja-themed first transformation. He is armed with two sword-like Slismashers (スライスマッシャー, Suraisumasshā) and can create illusions of himself from the two lantern-like Mirage Summoners (ミラージュサモナー, Mirāju Samonā) on his shoulder pads. His Smash essence was collected and purified to make the Ninjya Fullbottle.
• Square Smash (スクエアスマッシュ, Sukuea Sumasshu): Nabeshima's cube/comic panel-themed second transformation upon his kidnapping by Blood Stalk. He is armed with a pen-like blade on his right arm called the Area Cut Pen (エリアカットペン, Eria Katto Pen), which can create portals to attack from behind, slice through large buildings with a single cut and create blocks from various materials. He was used by Blood Stalk to lure Build and was enlarged before being defeated. His Smash essence was collected and purified to make the Comic Fullbottle.

Masahiro Nabeshima is portrayed by Ichi Omiya (市オオミヤ, Ichi Ōmiya).

Eita Kawai

Eita Kawai (河合 栄多, Kawai Eita) is a researcher in the Touto Institute and one of Katsuragi's sympathizers. He uploaded data of Pandora Box before the Faust army stole it. Blood Stalk transformed him into the Press Smash Hazard (プレススマッシュハザード, Puresu Sumasshu Hazādo) to fight Ryuga Banjo, but he was easily defeated. A weakened Kawai was reverted to his human form by Stalk, who erased his memories and altered his face to look like Kuwata.

Eita Kawai is portrayed by Tsukasa Honjo (本庄 司, Honjō Tsukasa).

Shingo Kuwata

Shingo Kuwata (桑田 真吾, Kuwata Shingo) is a Touto Institute researcher and a Katsuragi sympathizer. He uses his Fullbottle to become a version of the Flying Smash. After being defeated by Build, he reveals that he was meant to lure Build away from Faust's raid to steal the Pandora Box. Before committing suicide, he reveals that Takumi had been faking his death.

Shingo Kuwata is portrayed by Ryo Yoshida (吉田 亮, Yoshida Ryō).

Guardians

The Guardians (ガーディアン, Gādian) are enforcement androids mass-produced by Namba Industries as peacekeepers of each country, though it is not initially known that they are supporting governments outside Touto. They also act as Faust sleeper agents awaiting activation by Blood Stalk.

They are armed with the Safeguard Rifles (セーフガードライフル, Sēfugādo Raifuru) and ride motorcycles called Capital Roaders (キャピタルローダー, Kyapitaru Rōdā). A large number of them can combine together to form a single gigantic robot equipped with multiple guns. Under Faust's servitude, the reprogrammed Guardians can act as suicide bombers.

Namba Heavy Industries

Namba Heavy Industries Ltd (難波重工, Nanba Jūkō) is a company established by Jūzaburō Namba which provides financial support to Faust. Because of its pervasive influence, all three countries attempted to distance themselves from Namba, although the company has agents placed within the governments' infrastructures. After Evolto murdered and assumed the identity of Seito Prime Minister Midō, Namba Heavy Industries uses Seito's resources to launch an invasion of Touto and construct the Pandora Tower (パンドラタワー, Pandora Tawā) to create an empire with the Pandora Box. However, Evolto uses them as pawns and destroys the company.

Jūzaburō Namba

Jūzaburō Namba (難波 重三郎, Nanba Jūzaburō) is the corrupt and war-mongering chairman of Namba. He initially collaborates with Faust and Evolto to acquire the Build system for military applications, but has a secret agenda to use the Pandora Box's energy to create weapons of mass destruction. He also brainwashed children to act as his agents, including Sawa Takigawa. A power-hungry man with a god complex, he will do anything to attain his goals. However, he is not completely cruel as he was shown to be close to Nariaki Utsumi in flashbacks.

His ultimate goal is to use the power of the Pandora Box to reform Japan, and eventually the entire world, under his rule and in his image. However, Evolto exploited him for its own agenda. Namba then requests aid from the Kamen Riders against Evolto, but they fail and Namba is killed by Evolto while begging for his life.

In the merged universe at the end of the series, an alternate Namba owns a metalworking factory known as Namba Machine Workshop (難波機械製作所, Nanba Kikai Seisakusho), rather than a huge weapons manufacturer.

Jūzaburō Namba is portrayed by Akira Hamada (浜田 晃, Hamada Akira), while Norimasa Fuke portrays Namba's disguise as Masakuni Midō.

Namba Children

The Namba Children (難波チルドレン, Nanba Chirudoren) are scientists, soldiers and spies who were brainwashed by Jūzaburō Namba from an early age. They are positioned as sleeper agents within Touto, Hokuto and Seito to inform for Namba while acquiring whatever Namba needs.

Nariaki Utsumi

Nariaki Utsumi (内海 成彰, Nariaki Utsumi) is the 28-year-old secretary of Himuro who was formally a Touto Institute scientist. Despite his commitment to Faust, Gentoku and Namba Heavy Industries, Utsumi expresses regret over his life choices, even commenting to Sento about their similar predicaments. To conceal Faust's activities, Utsumi became a scapegoat by masquerading as Night Rogue. His attempted suicide is stopped by Sento, but Utsumi is gravely injured and converted into a cyborg by Evolto. Utsumi then returned to Namba as his spokesperson and developed the Rider Systems for Hokuto and Seito, gathering data on the Hazard Trigger while perfecting the Kaiser System. Although he seemed to become more open-minded, Utsumi was actually a callous sadist and completely loyal to Namba.

After Evolto turns on Namba and killed him, Utsumi faked losing his sanity and was recruited as Evolto's enforcer, Kamen Rider Mad Rogue, briefly serving as a host to a fragment of the alien's body. But as Evolto neared his end goal, Utsumi reveals his deception and allies himself with Gentoku to avenge Namba while destroying Evolto's replicas of the Washio Brothers. Though his cybernetics burn out as Evolto defeats him, Utsumi sacrifices himself to shield Gentoku and Sawa from the alien's attack.

After the worlds are merged at the end of the series, an alternate Utsumi is shown working in Namba's metalwork factory. In Build New World: Kamen Rider Cross-Z, when Killbus restored the Pandora Box, Utsumi's lack of Nebula Gas administration prevented him from regaining the memories of his alternate self. But despite that, in Build New World: Kamen Rider Grease he recovers the memories of his alternate self along with his powers of Kamen Rider through the injection of Nebula Gas, assisting the other Riders in their battle against Down Fall.

Utsumi twice became Night Rogue as a decoy. His modification on Night Rogue grants him the ability to analyze his opponent through his visor. As the creator of the perfected Kaiser System, Utsumi is able to transform into Hell Bros using the Nebula Steam Gun. As Hell Bros, his main weapon is the Nebula Steam Gun and the Steam Blade.

With the Evol-Driver Utsumi can become Kamen Rider Mad Rogue (仮面ライダーマッドローグ, Kamen Raidā Maddo Rōgu) by using the Bat (バット, Batto) and Engine (エンジン, Enjin) Fullbottles the Evol-Driver's Evol Match (エボルマッチ, Eboru Matchi) scrambles both elements of Fullbottles into a symmetrical form and his is specially tuned for human use. As Utsumi was planning to betray Evolto from the beginning, his Evol-Driver was modified to imitate Evolto's Phase evolution but the full power was too much for his cybernetics to handle. His finisher is the Evoltic Attack (エボルテックアタック, Eborutekku Atakku), which can be performed by channeling either his main Fullbottles or a different Fullbottle without changing his form. In a similar vein to Evolto, Mad Rogue is also possesses a Rider Evol-Bottle, allowing him to use Creation and manifest the power of a single Fullbottle.

• Pirates (パイレーツ, Pairētsu): By inserting the Kaizoku Fullbottle, Mad Rogue can summon the Kaizoku Hassyar which allows him to perform the Pirates Finish (パイレーツフィニッシュ, Pairētsu Finisshu) finisher.

Nariaki Utsumi is portrayed by Yuki Ochi (越智 友己, Ochi Yūki). As a child, Utsumi is portrayed by Yusei Ohtake (大竹 優青, Ōtake Yūsei).

Masuzawa

Masuzawa (増沢) is a spy who works as secretary to the Touto prime minister. When he is exposed by Sento, he kills himself using a Fullbottle to avoid capture. He is responsible for slipping a listening device into the Dragon Fullbottle to spy on Sento.

Masuzawa is portrayed by Taro Nakatani (中谷 太郎, Nakatani Tarō).

Washio Brothers

The Washio Brothers (鷲尾兄弟, Washio Kyōdai) are a pair of siblings from Seito who serve alongside Gentoku as Seito's main troopers. The indoctrination and training they received transform them into sadistic soldiers who use deception and dirty tricks to accomplish their tasks. They transform using the Kaiser System developed by Kaisei Mogami and Nariaki Utsumi, with a shared Nebula Steam Gun (ネビュラスチームガン, Nebyura Suchīmu Gan). Because of their limited supply in weaponry, the Nebula Steam Gun's Rifle Mode (combined with the Steam Blade) can only be held by one of them while the other engages in hand-to-hand combat.

After Evolto declared war against Namba Heavy Industries, the Washio Brothers form an uneasy alliance with the Riders before losing their lives. Evolto created his own copy of the Washio Brothers' Kaiser forms as guardians at the Pandora Tower. Utsumi revealed that he had sabotaged the Kaiser Systems and programmed both Same and Bike Fullbottles as countermeasures, used by Rogue and Mad Rogue to destroy the copies.

• Fū Washio (鷲尾 風, Washio Fū): The older brother who uses the Gear Remocon (ギアリモコン, Gia Rimokon) to transform into Remocon Bros (リモコンブロス, Rimokon Burosu), a turquoise-colored version of Kaiser. He is the dominant user of Nebula Steam Gun. He can use his Gear Remocon with Rai's Gear Engine to transform into Hell Bros (ヘルブロス, Heru Burosu), an upgraded version of Bi-Kaiser. Despite being the more level-headed of the two, he occasionally shows annoyance and fury. Fū sacrificed himself to shield Cross-Z from a deathblow. Fū Washio is portrayed by Osamu Adachi (足立 理, Adachi Osamu). As a child, Fū is portrayed by Shinta Takaiwa (高岩 芯泰, Takaiwa Shinta).
• Rai Washio (鷲尾 雷, Washio Rai): Fū's younger brother who uses the Gear Engine (ギアエンジン, Gia Enjin) to transform into Engine Bros (エンジンブロス, Enjin Burosu), a white-colored version of Kaiser Reverse. As Remocon is the primary user of Nebula Steam Gun, Engine uses the Steam Blade as his main weapon. Engine Bros is the most vulnerable of the pair and can be weakened with water-based attacks. Rai is short-tempered, careless and more violent in combat. During an alliance with the Riders against Evolto, Rai was the first to be killed and was caught in their former companion's black hole, giving his Gear Engine to Fū before his death. Rai Washio is portrayed by Yuudai Nasuda (奈須田 雄大, Nasuda Yūdai). As a child, Rai is portrayed by Taiga Watanabe (渡辺 虎雅, Watanabe Taiga).

Other versions of Hell Bros also existed in the series' spin-offs:

• Nebula Hell Bros (ネビュラヘルブロス, Nebyura Heru Burosu) is an incomplete version of Hell Bros, lacking both Engine and Remocon components, leaving its only weapon the Nebula Steam Gun. He was an unnamed civilian forcefully experimented upon by Namba Heavy Industries. While leading an army of Faust's Guardians to steal Touto's Fullbottles, he was confronted and defeated by Build.
• Clone Hell Bros (クローンヘルブロス, Kurōn Heru Burosu) is a copy of the Hell Bros and the prototype for Clone Smash. Utsumi sent it to fight against Kamen Rider Build's SameBike Form to test its capabilities. Sometime after the Clone Smash were mass-produced, Utsumi programmed the SameBike Form's Fullbottles as the main weakness to the new Kaiser Systems.

Hard Guardians

The Hard Guardians (ハードガーディアン, Hādo Gādian) are enhanced versions of the Guardians which Namba Heavy Industries mass-produced following Seito's war declaration on Touto. When Namba Heavy was disbanded, the remaining units were under control of Evolto and served as the front line of Pandora Tower's defense.

The Hard Guardians are equipped with a combat AI unit, right arm-mounted gatling-guns, left-arm-mounted clawed gauntlets, and shoulder-mounted missile pods. An improved drive module was placed on each joint to provide enhanced mobility. Their equipment can be replaced depending on the combat situation and can fight on equal terms against Rider Systems users.

Katsuragi family

Takumi Katsuragi

Takumi Katsuragi (葛城 巧, Katsuragi Takumi) is 26 years old and the past identity of Sento Kiryu, infamously known among his peers as "The Devil's Scientist" (悪魔の科学者, Akuma no Kagakusha). During the Sky Disaster, unaware of the full truth at the time, Takumi promised his father Shinobu that he would stop the Blood Race from destroying the Earth and restarted Project Build (プロジェクトビルド, Purojekuto Birudo) where he subjected himself to Nebula Gas to become Kamen Rider Build, only to be banned for conducting unethical human experimentations with the Nebula Gas to evolve humanity.

During this period, Takumi assisted his former Touto colleague Kaisei Mogami in building the Enigma system to travel to another reality. While testing the performance of Kamen Rider Build in said world, he twice intervened in the confrontation between humans and Bugster. Having accidentally killed Kamen Rider Genm prior, Build went on to extract Ex-Aid's samples into a single Fullbottle before foiling Mogami's intent to cause a convergence between the two realities and stopped him.

Sometime after developing both Rider and Transteam Systems, Takumi learned that Faust had been compromised by Evolto. He halted the development of the Sclash Driver system and attempted to kill Evolto but was outsmarted. His memories and appearance were changed to Sento, and he was manipulated into completing the Rider System.

Takumi regained his memories when Evolto regained his perfect form, and becomes Build again but refuses to work with the others. When the Genius Fullbottle refused to cooperate, he was visited by Sento's consciousness and allowed this alter-ego to access Genius Form for the first time. From that point onward, Takumi served as a spiritual adviser to Sento despite his sense of pessimism.

Following the worlds' convergence, as revealed in Build New World: Kamen Rider Grease, Takumi exists as a separate being from Sento in their new universe and works despite being plagued by unpleasant memories of the old world.[2] Alongside Sento, he creates a special serum that enables the Rider System users to recover the ability to transform and to be immune to the Phantom Crushers' special ability. After Downfall is defeated, Takumi returns to the Japan Institute of Advanced Matter Physics (国立先端物質学研究所, Kokuritsu Sentan Busshitsugaku Kenkyūjo).

As the true creator of Build's Rider System, Takumi can use the basic Best Match forms. As he was absent while Sento further developed Build, Takumi had to retool it to keep up with its performance.

Takumi Katsuragi is portrayed by Yukiaki Kiyama (木山 廉彬, Kiyama Yukiaki), whereas his cameo appearances as Build in Kamen Rider Ex-Aid were voiced by Atsuhiro Inukai, Sento's actor.

Shinobu Katsuragi

Shinobu Katsuragi (葛城 忍, Katsuragi Shinobu) is the father of Takumi Katsuragi and a member of the Kiwami Project which saw Sōichi Isurugi come into contact with the Pandora Box. Shinobu conducted illegal research on an infant Ryuga. Later, Shinobu led the conference of the Pandora Box's discovery when Evolto caused the Skywall Disaster, and his reputation was ruined as he was used as a scapegoat. Shinobu faked his suicide soon after cryptically informing Takumi that Ryuga is essential to stop Evolto and his kin, enlisting Reika Kine's aid in smuggling himself out of Touto.

Shinobu secretly aided Evolto for ten years by using his research in an attempt to repair the Evol-Driver before Takumi found and hid it. Shinobu also developed a man-made variant of Fullbottles called Lost Fullbottles (ロストフルボトル, Rosuto Furubotoru), also referred to as Lost Bottles (ロストボトル, Rosuto Botoru) for short, which allow the user to transform into a Lost Smash with side-effects of heightened aggression and suggestibility. Shinobu resurfaces while Sento and his allies are searching for the Lost Fullbottles, revealing his alliance with Evolto while alienating Sento. However, Shinobu's plan was to eliminate the alien, pretending to be Evolto's ally while creating a specialized Best Match combination that could defeat the alien. He reveals his intentions to Sento when he thought Evolto had been defeated, but Evolto recovered and fatally wounds Shinobu. Shinobu lives long enough to give Sento his data to finalize the Cross-Z Build Form and apologize for hurting him. He comes back to life and like his son, he works as a scientist in the Japan Institute of Advanced Matter Physics in the new world. In Build New World: Kamen Rider Grease he created a copy of the Build Driver, which was owned by the Japanese government before being stolen by Downfall. After Downfall is defeated, he apologizes to Takumi for using him in the old world.

As the founder of Rider System, Shinobu possesses his own copy of the Build Driver and a set of Fullbottles to transform into another Kamen Rider Build. While having access to Best Match forms, Shinobu is capable of outmaneuvering the strongest of his opponents in one-on-one fights though he has difficulty fighting multiple opponents. He can also use another Fullbottle's power without transitioning, such as the use of Phoenix Fullbottle as an escape while still in Rabbit Tank form.

Shinobu Katsuragi is portrayed by Zyouzi Kokubo (小久保 丈二, Kokubo Jōji).

Kyōka Katsuragi

Kyōka Katsuragi (葛城 京香, Katsuragi Kyōka) is Takumi's mother and Shinobu's wife who was abducted from Hokuto and transformed by Faust into the first Strong Smash Hazard (ストロングスマッシュハザード, Sutorongu Sumasshu Hazādo). She was purified by Build, with the extracted element purified to create the Lock Fullbottle, before she entrusted the flash drive that contains the information of the Project Build to Sento.

Kyōka Katsuragi is portrayed by Hiro Komura (古村 比呂, Komura Hiro).

Prime ministers

As a result of the Skywall Disaster (スカイウォールの惨劇, Sukaiwōru no Sangeki) in 2007, Japan has been divided into three different districts: Touto, Hokuto and Seito. It was suspected that everyone present at the event become much more aggressive after being exposed to the Skywall's Nebula Gas. As a result of the separation, several foreign powers have attempted to take advantage of the situation although none of the districts display interest in allying with external forces. After Sento merges the world into a new reality at the conclusion of the series, an alternate Taizan has been elected prime minister of an undivided Japan with the other two as his ministers of welfare and finance respectively.

Taizan Himuro

Taizan Himuro (氷室 泰山, Himuro Taizan) is the 67-year-old father of Gentoku and the prime minister of Touto (東都, Tōto), a pacifist state with only enough military strength for self-defense. Despite the rivalries, Taizan wishes for Japan to reunite. Due to his poor health, he sent his son Gentoku to the unveiling of the Pandora Box, and retained his sanity as the only leader not affected by its radiation. Taizan suffered a heart attack during Faust's raid on Touto facility, and entrusted Gentoku as acting prime minister, unaware that Gentoku is high-ranking Faust-member Night Rogue. The Touto government was then compromised until Sento and Ryuga defeated Night Rogue, exposing his identity to Taizan who then orders his son to be taken into custody. Sōichi later poisoned Taizan which once again gives Gentoku emergency power to rule Touto. Taizan eventually recovered through Misora's power and exiled Gentoku while looking for a way to end the war with the least bloodshed. Taizan believes there is still good in Gentoku and vows to return his son.

As Namba and Stalk enact their plan to bring humanity into chaos, Taizan is kidnapped by Gentoku so Stalk can force Sento into reviving the original Project Build. Gentoku was already planning to save his father, working with the Kamen Riders against Evolto, but the plan backfires and Evolto transforms into Kamen Rider Evol. Taizan becomes the first victim of Evolto, sacrificing his life to save Gentoku from the alien. This act allows Gentoku to fully revert to his true self.

Taizan Himuro is portrayed by Meikyo Yamada (山田 明郷, Yamada Meikyō).

Yoshiko Tajimi

Yoshiko Tajimi (多治見 喜子, Tajimi Yoshiko) is the 53-year-old prime minister of Hokuto (北都), a social welfare state which puts the needs of its people above all else. The Skywall Disaster rendered most of the farmland infertile with the resulting economic collapse forcing many citizens to take their children out of school. Tajimi's personality was affected by radiation from the Pandora Box, and she secretly directed government funds from social welfare to the military. The machinations of Sōichi, Namba and Gentoku cause war between the other two countries to take the Pandora Box by force, and she declares war on Touto. Her ruthless behavior during the invasion disgusts Kazumi as he threatens her to stop targeting innocent civilians.

During Touto's fight against Hokuto, Tajimi acts on Sōichi's advice to station her entire military on Touto's border to invade if Grease was defeated. But Tajimi realized she had been manipulated into leaving her nation vulnerable to Seito, which invade and take her into custody. She is later brainwashed by Evolto, transforming her into the Owl Lost Smash (オウルロストスマッシュ, Ōru Rosuto Sumasshu) before being defeated and freed by Kamen Rider Build's Genius Form. This purified Tajimi's mind leaving her horrified and remorseful over everything she had done while being the only surviving prime minister.

Yoshiko Tajimi is portrayed by Ryoko Gi (魏 涼子, Gi Ryōko).

Masakuni Midō

Masakuni Midō (御堂 正邦, Midō Masakuni) is the 61-year-old prime minister of Seito (西都), which seeks economic recovery through technical advancement, sending its young adults across the world to gather technical knowledge. Midō expressed an interest in Tajimi's offer for alliance, but stood by while Hokuto and Touto weakened each other in warfare. When Hokuto lost to Touto, Midō sends Seito's military to invade Hokuto, taking over the country and capturing Tajimi. However, Midō is also a nervous man as shown by his reaction during the Touto-Seito proximity match.

After losing the fight against Touto, Midō keeps his agreement with Touto while falling out with Namba, resulting in his death by Evolto. The alien then had Namba assume Midō's identity to use the country for Namba Heavy Industries' operations and his future plots. Evolto later poses as Midō during his endgame plan and places his kinsmen into governor positions.

Masakuni Midō is portrayed by Norimasa Fuke (冨家 規政, Fuke Norimasa).

Vernage

Vernage (ベルナージュ, Berunāju) is the former queen of Mars who survived the destruction of her civilization at the cost of her physical form. She managed to seal Evolto along with his Evol-Trigger into the Pandora Box, while separating his Evol-Driver to prevent him from using it inside the box to free himself. When the artefacts were returned to Earth, her spirit was preserved in a bracelet which latched onto a young Misora. Ten years later, Vernage's consciousness slowly awakened and occasionally rescued the Kamen Riders from Namba's forces.

As her spirit resided within Misora's bracelet, she provided the young girl with the ability to purify Nebula Gas. The process caused Vernage's memories of her civilization's destruction to play within Misora's mind. Although presented as a powerful entity, she pointed out that her life force is diminishing. Vernage left Misora's body to restore girl's humanity while she was transformed into CD Lost Smash, and transferred herself into Ryuga to counteract the psychological effects from the trace remnants of Evolto's genes. Vernage passed away after Evolto's death, having fulfilled her goals.

Vernage is voiced by Sora Amamiya (雨宮 天, Amamiya Sora).

Blood Tribe

Blood Tribe (ブラッド族, Buraddo Zoku) are a mysterious race of extraterrestrial origin who originated from Planet Blood (ブラッド星, Buraddo-sei) before it was destroyed by their ruler Killbus. Led by Killbus's younger brother Evolto, the four surviving Blood members caused the downfall of the Martian civilization and many other planets before possessing the four astronauts sent to explore Mars. While Evolto is the antagonist of the series after possessing Sōichi Isurugi, the other three Blood Tribesmen who possessed Sōichi's fellow astronauts supported Evolto from behind the scenes before making their presence known in the events of Kamen Rider Build the Movie: Be the One. Evolto used his guise as Midō to arrange for his tribesmen to become governors in Japan's three regions, only for them to mutiny and attempt to destroy Earth on their own through the Build Annihilation Plan (ビルド殲滅計画, Birudo Senmetsu Keikaku): Acquiring Sento's Hazard Trigger and use it with the Pandora Box to destroy Earth's core. But after his kin were destroyed and his defeat by the Kamen Riders, Evolto is the only remaining survivor in the new world.

Evolto

Evolto (エボルト, Eboruto) is the true antagonist of the series and leader of both the Blood Tribe and Faust. A genocidal sociopath, prior to the series, Evolto has taken the Pandora Box away and escaped from his brother, Killbus who was using Pandora Box to destroy his home planet. After the destruction of his planet, he used the power of the Pandora Box to destroy planets to absorb their energies as a means of gaining power and travelling. Until he destroyed the Martian civilization, he was rendered incorporeal and lost his true physical form before Vernage sealed him alongside his damaged Evol-Trigger within the Pandora Box.

When a Mars rover arrived for observation, Evolto used it to send a piece of himself to Earth to acquire a host to restore himself. But it backfired when the fragment's attempt of possessing Namba Industries security guard Yuri Banjo resulted in it being assimilated into her unborn child Ryuga. 13 years later, Evolto possessed the astronaut Sōichi Isurugi when he retrieved the Pandora Box from Mars and attempted to destroy Earth, only for Vernage's intervention to result in the Skywall Incident to scatter the Pandora Box across Japan. This forces Evolto to execute a decade-long plan of manipulating various individuals and events, such as the foundation of Faust, positioning himself within Namba Heavy Industries and grooming Ryuga as his next vessel. Evolto also used Sōichi's connections to force Shinobu and his son into working for him, tricking a young Misora to purify Fullbottles, and framed Ryūga for Tarō's death while an unconscious Katsuragi was spirited away with his memory and face altered. With Katsuragi's new identity as "Sento Kiryu", Evolto further manipulated him into perfecting the Build System and created other Rider Systems that Katsuragi purposely scrapped. In the hopes of hiding his presence, he made his original voice the default setting of Blood Stalk's system during transformation.

After all Fullbottles were purified, Evolto exposed his treachery to the crews of Nascita and his plans to use the Pandora Box to destroy Earth's civilizations, exploiting Namba as they engineered a series of schemes to take over Japan with only Touto and its Kamen Riders as their opposition. After regaining the Evol-Driver, Evolto abandoned his host to become Kamen Rider Evol (仮面ライダーエボル, Kamen Raidā Eboru) as he transferred himself to Ryūga's body to regain his full power and then into Sento to use his intelligence to repair the Evol-Trigger. Once the Evol-Trigger was repaired, Evolto left Sento's body and became a corporeal shapeshifter, assuming Sōichi's appearance. Evolto then proceeded to kill Namba who refused to accept being a puppet ruler while winning the maddened Utsumi to his cause. Evolto decided to take over Earth instead of destroying it after finding amusement in Namba's final moments and Utsumi's descent into insanity. Initially limited to feeling either delight or irritation, Evolto developed human emotions as a result of his Hazard Level increasing. Evolto also assumed Midō's identity to place the Blood Tribe as governors to execute Build Annihilation Plan, but a mutiny by Inō forced him into an alliance with his own adversaries.

When later defeated by the four Kamen Riders using a coordinated attack, Evolto imparts a fragment of himself within Utsumi to reconstitute himself. He then kills Shinobu while reclaiming his Evol-Driver and regaining his full strength, before splitting off a part of himself to possess Kazumi to steal back the CD Lost Fullbottle for the Last Pandora Panel Black (ラストパンドラパネルブラック, Rasuto Pandora Paneru Burakku). He then absorbs the panel to assume his true monstrous form, but was forced back to his Rider Form by the four Kamen Riders and loses a Lost Fullbottle as well, though he escapes. Combined with his inability to emotionally compose himself, Evolto became very disappointed by the defeat and falls back to his original plan of destroying all life on Earth. As the final battle between Evolto and the Riders began, he succeeds in causing Kazumi's death and kills Utsumi after the latter reveals his true allegiance. Evolto becomes omnipotent but Gentoku wounds him enough for Ryūga to sacrifice himself to trap Evolto in the vortex of a wormhole created by the complete Pandora Box.

Evolto attempts to cheat death by absorbing Ryuga but Sento saves his friend, with Evolto seemingly erased as a side-effect of Pandora Box merging their universe with the prime Kamen Rider universe. However, Evolto reconstitutes himself through a fragment of himself that slipped into Ryuga. When Killbus reappears again in the new world and threatens to destroy the entire universe, Evolto gracefully joins forces with Ryūga to defeat Killbus before leaving Earth to regain his full strength and body.

A cruel, fierce, and ruthless character, Evolto committed several heinous acts using Sōichi's body as a vessel, killing without hesitation and on one occasion turned a child into a Smash, with his plots and actions resulting in several deaths. Evolto is a very patient manipulator, having spent years establishing his plans while winning allies or placing enemies in situations that play to his advantage, but can be taken off guard by unexpected occurrences where he was forced to improvise. Due to the successful nature of his plots in the first half of the series, Evolto becomes arrogant and overconfident, but his reliance on luck backfired several times. It also extends to his tendency of toying with his opponents as he fails to expect a stronger counterattack, which proves costly when the Riders were able to force him out of his true form just moments after he had regained it. Another flaw Evolto suffered was his inability to handle human emotions as the result of having used multiple host bodies and his exposure to Build, making him prone to blind rage and later expressing fear when sucked into the wormhole and facing his impending doom. In the new world, while still resentful toward the Kamen Riders and humanity, Evolto admits to having developed a new-found respect for them as he mocked Killbus for underestimating humans right before the latter is finished off by Cross-Z Evol.

As Kamen Rider Evol, Evolto uses the Evol-Driver (エボルドライバー, Eboru Doraibā) and Evol-Bottles (エボルボトル, Eboru Botoru), from which the Build System was reversed engineered. As a Rider, Evol has high-speed movements on par with any previous Kamen Riders, matched only by Build Genius Form. Evol's finisher is the Evoltic Finish (エボルテックフィニッシュ, Eborutekku Finisshu). Each of his forms are treated as evolution of his Phases (フェーズ, Fēzu):

• Cobra Form (コブラフォーム, Kobura Fōmu) is the primary form of Evol, a.k.a. "Phase 1" (フェーズ1, Fēzu Wan), and accessed with the use of Cobra Evol-Bottle. Evol is capable of secreting enhanced poisons and is able to outmaneuver his opponents with blinding speed.
• Dragon Form (ドラゴンフォーム, Doragon Fōmu), a.k.a. "Phase 2" (フェーズ2, Fēzu Tsū), was accessed when Evol possessed Ryuga and created the corresponding Dragon Evol-Bottle from his body. Aside from adding Cross-Z's Beat Closer to his arsenal, Evol can also use pyrokinesis. This form was lost after Ryuga stole the Dragon Evol-Bottle and used it to transform into Great Cross-Z.
• Rabbit Form (ラビットフォーム, Rabitto Fōmu), a.k.a. "Phase 3" (フェーズ3, Fēzu Surī), was accessed when Evol possessed Sento and created the corresponding Rabbit Evol-Bottle from his body. The result of both Sento's gambit in raising his Hazard Level to 6 and self-destruction with a Pandora Panel concluded in his possession and the change of his hair color to white. In addition to Build's Drill Crusher, Evol gains a sharp increase in acceleration and agility.
• Black Hole Form (ブラックホールフォーム, Burakku Hōru Fōmu) is Kamen Rider Evol's true form, a.k.a. "Phase 4: Perfection" (フェーズ4: 完全体, Fēzu Fō: Kanzen-tai), accessed through the use of Cobra Evol-Bottle and the Evol-Trigger (エボルトリガー, Eboru Torigā). This form was previously sealed by Vernage during their battle on Mars, until the energies from the combined attack of Cross-Z Magma, Grease and Rogue were exploited to restore the Evol-Trigger which then restored his corporeal form. Incredibly powerful, Evol can manipulate black holes and destroy celestial bodies. Before his arrival on Earth, Evol had once brandished an energy blade in a fight against Vernage.

As the Rider (ライダー, Raidā) Evol-Bottle invokes every transformation, it can also use Creation (クリエーション, Kuriēshon) when in conjunction with a normal Fullbottle.

• Kikanhou (機関砲, Kikanhō, Autocannon): By inserting the Gatling Fullbottle, Evol can summon the Hawk Gatlinger, allowing him to perform the Kikanhou Finish (機関砲フィニッシュ, Kikanhō Finisshu) finisher.

By activating the Evol-Trigger's Feverflow (フィーバーフロー, Fībāfurō) mode while obtaining all ten Lost Fullbottles stacked in the black Lost Panel merged with himself, Evolto gains the ability to assume his true Monstrous Form (怪人態, Kaijin-tai). His signature ability is the Black Hole Break (ブラックホールブレイク, Burakku Hōru Bureiku), which allows him to assimilate celestial bodies as he consumed the moon and part of Earth to assume his Ultimate Form (究極態, Kyūkyoku-tai) with access to the Evolti Voider (エボルティヴォイダー, Eboruti Voidā) shoulder units and Evolti Grasper (エボルティグラスパー, Eboruti Gurasupā) gauntlets. But while it is Evolto's strongest form, the Evol-Trigger also becomes his weak point as Gentoku dies removing it to give Build and Cross-Z their chance to destroy the alien.

Evolto is voiced by Tetsuo Kanao (金尾 哲夫, Kanao Tetsuo). While possessing Sōichi Isurugi and later assuming his likeness, he is played by Yasuyuki Maekawa.

Kengo Inō

Kengo Inō (伊能 賢剛, Inō Kengo) is Evolto's second-in-command who served as advisor to Seito Prime Minister Midō and influenced Sento meeting Ryuga, later becoming governor of Touto by the events of Kamen Rider Build the Movie: Be the One, after the Japanese civil war had ended. He then leads a mutiny against Evolto to carry out the Blood Tribe's initial plan to destroy Earth, Inō using the Tokyo populace's anti-Kamen Rider sentiment to hypnotize them into hunting down Sento with an infected Ryuga made into his personal agent. Once acquiring the Hazard Trigger to enable his transformation into Kamen Rider Blood, Inō later acquires the Pandora Box to proceed to travel down to Earth's core and destroy the planet from the inside-out. But he is destroyed by Kamen Rider Cross-Z Build.

Possessing the Cobra Lost Fullbottle, Inō uses it with Ryuga's Build Driver and Great Cross-Z Dragon, combined with Sento's Hazard Trigger to transform into Kamen Rider Blood (仮面ライダーブラッド, Kamen Raidā Buraddo). The form initially requires him to absorb nearby Blood Tribesmen, including Ryuga for possessing Evolto's essence, before Build extracted the absorbed targets from his body. Blood rivals the strength of Build's Genius Form and can summon energy cobras as reinforcements.

Kengo Inō is portrayed by Masanobu Katsumura (勝村 政信, Katsumura Masanobu).

Mitsuomi Gōbara

Mitsuomi Gōbara (郷原 光臣, Gōbara Mitsuomi) is a member of Blood Tribe and a former advisor to Hokuto Prime Minister Tajimi, having orchestrated Kasumi Ogura's conversion into a Smash, before becoming the new governor of Seito. He can transform into Zebra Lost Smash (ゼブラロストスマッシュ, Zebura Rosuto Sumasshu) using the Shimauma (シマウマ, Zebra) Lost Fullbottle. He was defeated by Kamen Rider Grease after initially defeating him in their first encounter.

Mitsuomi Gōbara is portrayed by Takashi Fujii (藤井 隆, Fujii Takashi).

Ryōka Saiga

Ryōka Saiga (才賀 涼香, Saiga Ryōka) is a female member of Blood Tribe and a former aide to Touto Prime Minister Himuro before becoming the new governor of Hokuto. She can transform into Scissors Lost Smash (シザーズロストスマッシュ, Shizāzu Rosuto Sumasshu) using the Hasami (ハサミ, Scissors) Lost Fullbottle. She is defeated by Kamen Rider Rogue after initially defeating him in their second encounter.

Ryōka Saiga is portrayed by Rena Matsui (松井 玲奈, Matsui Rena).

Killbus

Killbus (キルバス, Kirubasu) is the older brother of Evolto and the Build New World: Kamen Rider Cross-Z, a suicidal hedonist who ruled Planet Blood before destroying it as part of his plan to use the Pandora Box to destroy the entire universe along with himself. Using the form of a famous dancer named Satoshi Kakizaki after appearing from the Last Pandora Panel White (ラストパンドラパネルホワイト, Rasuto Pandora Paneru Howaito), Killbus hunts Evolto within Ryūga to restore the Pandora Box and seeks to absorb Ryuga and Evolto into the white panel to obtain enough energy to destroy the universe. He is later defeated by Ryūga in the Cross-Z Evol form.

By inserting the Killbuspider (キルバスパイダー, Kirubasupaidā) (Sento's robotic spider-like pet converted into a transformation item by Killbus) loaded with the Killbus Spider (キルバススパイダー, Kirubasu Supaidā) Fullbottle into Sento's Build Driver, Killbus transforms into Kamen Rider Killbus (仮面ライダーキルバス, Kamen Raidā Kirubasu). Killbus transformed into Build before adopting his personal Rider namesake. By himself, Killbus can use Drill Crusher and Kaizoku Hassyar as his weapons and summon Hazard Smash clones.

Killbus is voiced by Anri Katsu (勝 杏里, Katsu Anri). While assuming the forms of Sento Kiryu and Satoshi Kakizaki, he is portrayed by Atsuhiro Inukai and Gaku Shindo, respectively.

Smash

The Smash (スマッシュ, Sumasshu) are monsters formed by humans injected with the liquefied Nebula Gas (ネビュラガス, Nebyura Gasu) as part of Faust's experiments. The experimental subject loses almost all of their memories. To revert a Smash back to a normal human, the Kamen Riders must defeat them and extract their element liquids into an Empty Bottle (which can later be purified into a Fullbottle for their transformation and equipment uses). Faust agents are given their own Fullbottles to transform into their Smash forms, which are equipped with a self-destruct function. Silver-colored Smash are stronger versions, achieved through exposure to Nebula Gas of higher Hazard Levels.

The experiment's goal was to find a perfect candidate for the Build Driver, with the Smash transformations considered failures. Each victim is ranked by their tolerance of Nebula Gas called Hazard Levels (ハザードレベル, Hazādo Reberu).

• Hazard Level 1: Patients with frail body types, unable to survive any attempt to revert them to their human form.
• Hazard Level 2: Patients with the ability to survive the gas and transform into Smash. Those who rank above 2 can retain their human forms and were given the chance to raise their Hazard Levels through fighting experience.
• Hazard Level 3: Patients who completed their tolerance towards the gas. They are also considered suitable candidates for the Build Driver.
• Hazard Level 4: Compatible users of the Sclash Drivers. Patients in Level 3 can also reach this level by using the Build Driver with the Hazard Trigger.
• Hazard Level 5: Only Evolto's race can access this level, which is required to access the Evol-Driver.
• Hazard Level 6: Achieved by Build when he taps into the power of a Pandora Box's panel.
• Hazard Level 7: Humans in this level can strengthen certain Fullbottles with their own power.

The Smash monsters include:

• Fang Smash (ファングスマッシュ, Fangu Sumasshu) is a mandible-themed Smash and the first opponent of Build when Takumi was rendered amnesiac into his new identity, Sento. It was defeated off-screen as Build's first victory.
• The Needle Smash (ニードルスマッシュ, Nīdoru Sumasshu) is a hedgehog-themed Smash that can use his sharp, neurotoxin-filled fingernails, his arm blades, and his stretched back full of needles to attack. He is quickly defeated by Build, who extracts the Needle Smash's element liquid to refine into the Harinezumi Fullbottle.
• The Strong Smash (ストロングスマッシュ, Sutorongu Sumasshu) is a rock/gorilla-themed Smash who uses his bare hands to fight with vast physical strength, and can jump very high. He was originally Kyōichi Shimizu (志水 恭一, Shimizu Kyōichi), a lab assistant of Shinobu Katsuragi and one of Faust's captives. He was turned into the Strong Smash to retrieve Ryuga, who had escaped from Faust, and is defeated and restored by Build, though he suffers memory loss. The Strong Smash's element is later purified to make the Gorilla Fullbottle. Shimizu reappears in episode 41 under the control of Evolto, transforming into the Stag Lost Smash (スタッグロストスマッシュ, Sutaggu Rosuto Sumasshu) to fight the Kamen Riders. After his defeat, he is murdered by Evolto for attempting to give Sento information. Shimizu is portrayed by Shohei Yamazaki (山﨑 将平, Yamazaki Shōhei).
• The Burn Smash (バーンスマッシュ, Bān Sumasshu) is a dragon-themed Smash armed with the flamethrower-like Smash Burner (スマッシュバーナー, Sumasshu Bānā) on her right arm. She was originally Kasumi Ogura (小倉 香澄, Ogura Kasumi), Ryuga's 23-year-old girlfriend who was tricked by Nabeshima to send Ryuga to the scene of Katsuragi's death. Following Ryuga's escape with Sento's help, Mitsuomi Gōbara advised Evolto to reprogram the abducted Kasumi and convert her into a Smash that they send after Ryuga. Though traits of Kasumi's original personality resurface as she reveals what she knew of Faust, her illness made it impossible for her to regain her humanity with Build is forced to destroy her as a mercy kill. The Burn Smash's element is later purified into Dragon Fullbottle which Sento gives to Ryuga, with Sento giving Ryuga her will to provide him with the resolve to fight as Kamen Rider Cross-Z. Gentoku and Gōbara would later reveal to Ryuga that Kasumi's sacrifice was arranged by the Blood Tribe as a means of incentive to stimulate Ryuga's alien DNA. Following their universe's absorption into the prime universe, an alternate Kasumi is the girlfriend of the alternate version of Ryuga. Kasumi Ogura is portrayed by Risako Itō (伊藤 梨沙子, Itō Risako).
• The Flying Smash (フライングスマッシュ, Furaingu Sumasshu) is a scarecrow/hawk-themed Smash that can fly by controlling the surrounding air currents and attack using her Air Slash Claws (エアスラッシュクロー, Ea Surasshu Kurō). She was originally Reika Kine (木根 礼香, Kine Reika), the mother of Kōta Kine (木根 光多, Kine Kōta). After being turned back to human, the extracted Smash element was purified to make the Taka Fullbottle. Reika returns with her son to help Sawa and Ryuga alongside boatman Igarashi (五十嵐) who operates a boat she and her husband own. Reika returns in episode 40 where she reveals the role she and her husband played in smuggling Shinobu Katsuragi out of Touto after faking his death. Reika Kine is portrayed by Machiko Kochi (東風 万智子, Kochi Machiko).
• The Press Smash (プレススマッシュ, Puresu Sumasshu) is a machine press-themed Smash with powerful pressing mechanisms in each part of his body to attack and destroy enemies by compressing his arms. He was originally Tatsuya Kishida (岸田 立弥, Kishida Tatsuya), a friend of Tarō Satō since middle school; they had formed a musical band called Tsunageez (ツナ義ーズ, Tsunagīzu) and he believes Sento to be Tarō. Tatsuya is kidnapped by Blood Stalk and turned into the Press Smash as bait for Sento. Despite being returned to normal, he is turned back into a Smash by Ryuga to find Faust's secret location. His Smash form's Hazard Level was increased to cause it to self-destruct, until Build saved him during a raid on Faust. The Press Smash's element is later purified to make the Panda Fullbottle. Another Press Smash Hazard was sent by Hokuto to attack Touto; it was defeated by Build before being made human again. In the merged universe at the conclusion of the series, Tatsuya and a revived Tarō Satō are members of a music band. Tatsuya Kishida is portrayed by Pinboke Tarō (ピンボケたろう).
• The Ice Smash (アイススマッシュ, Aisu Sumasshu) is a Smash that can shoot Icicle Chill Arrows (アイシクルチルアロー, Aishikuru Chiru Arō). He was originally Takehiko (雄彦), a boy living in Hokuto who was transformed by Blood Stalk via the Steam Blade's 'Devil Steam'. He is purified by Build, although the stress from transforming into a Smash took a huge toll on his body. The Ice Smash's element is later purified to make the Shoubousha Fullbottle. Takehiko is portrayed by Sasuke Sasaoka (笹岡 サスケ, Sasaoka Sasuke).

Enhanced Smash (Hazards):

• The Strong Smash Hazard (ストロングスマッシュハザード, Sutorongu Sumasshu Hazādo) is an enhanced version of the Strong Smash. The first Strong Smash Hazard the Kamen Riders encountered had been Takumi's mother Kyōka Katsuragi. The second Strong Smash Hazard is a Touto soldier that Gentoku transformed and is defeated by Cross-Z. The third Strong Smash Hazard was sent by Hokuto to attack Touto before being defeated by Kazumi.
• The Stretch Smash Hazard (ストレッチスマッシュハザード, Sutoretchi Sumasshu Hazādo) is an enhanced version of the Stretch Smash. It was created by Gentoku to fight the Kamen Riders using one of two unnamed Touto soldiers. It targeted Misora who was caught in the battle before it was defeated and restored to human form.
• The Flying Smash Hazard (フライングスマッシュハザード, Furaingu Sumasshu Hazādo) is an enhanced version of the Flying Smash. It was sent by Hokuto to attack Touto. It was defeated by Build and Cross-Z before being made human again.

Clone Smash

The Clone Smash (クローンスマッシュ, Kurōn Sumasshu), unlike regular Smash, are created from pure Nebula Gas, and attack until destroyed. Being enhanced versions of the Press, Stretch, Strong and Flying Smash Hazard, the Clone Smash are stronger and more durable due to their inability to feel pain. The Clone Smash are later used as materials to power a Lost Fullbottle to enable its user's transformation into a Lost Smash.

Lost Smash

Lost Smash (ロストスマッシュ, Rosuto Sumasshu) are Smash breeds created by Evolto and Katsuragi as the final Smash evolution. The experiment includes a human victim being heavily dosed with Nebula Gas and transformed into the Lost Smash by absorbing a pair of nearby Clone Smash. Aside from heightened aggression and being easy to manipulate, they are also bound to die should they be defeated. The Genius Fullbottle of Kamen Rider Build has the ability to save these victims and remove traces of Nebula Gas.

The Lost Fullbottles created by Shinobu Katsuragi were used to invoke the target's transformation into Lost Smash. Their actual purpose is to complete the Lost Panel of Pandora Box to take control of humanity. The full set of Lost Fullbottles work differently depending on the Pandora Panels they slotted into: the Last Pandora Panel Black allows Evolto to regain his monstrous form by absorbing it, whereas its White counterpart can merge with five other Pandora Panels to fuse Earth with its alternate counterpart and avert the Skywall Disaster.

Kaisei Mogami

Kaisei Mogami (最上 魁星, Mogami Kaisei) is the main antagonist of Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider. A cyborg, Mogami was a researcher in the Touto Institute of Advanced Matter Physics and an associate of Takumi Katsuragi. Ten years earlier, while researching parallel universes, he found the Bugster Virus at the Skywall and concluded that the virus is from a parallel universe. He wanted to create the interdimensional gateway Enigma (エニグマ, Eniguma), but couldn't get funding so he moved to Namba Heavy Industries to continue his research. With Takumi's help, he developed both the Kaiser system and the Enigma which allowed him to make contact with the prime universe version of himself who is a Foundation X scientist. However, he lost the left side of his body due to an Enigma accident, caused by Takumi who opposed his ultimate goal. He resurfaces to cause the fusion and destruction of the two universes with the Enigma, to fuse with his counterpart and form a single immortal entity to become the ruler of all the universes. The two Mogamis form an alliance as they employ Foundation X's version of the Guardians known as the X Guardians (Xガーディアン, Ekkusu Gādian) while creating the Nebula Bugster strain. Both Mogamis eventually fuse, but their plans are foiled before being defeated by Ex-Aid and Build, the latter fulfilling their scheme to merge their dimensions months later while defeating Evolto.

Mogami is able to transform into the blue-colored Kaiser (カイザー, Kaizā), while his counterpart transforms into the red-colored Kaiser Reverse (カイザーリバース, Kaizā Ribāsu). They can also combine to form a single entity known as Bi-Kaiser (バイカイザー, Bai Kaizā). Utsumi managed to acquire the Kaiser System blueprints after Mogami's death and perfected the technology, which he gave to Seito as the developed Hell Bros gear used by the Washio brothers.

Kaisei Mogami is portrayed by Kenji Ohtsuki (大槻 ケンヂ, Ōtsuki Kenji).

Satoshi Kakizaki

Satoshi Kakizaki (柿崎 悟志, Kakizaki Satoshi) is a famous dancer whose form was copied by Killbus. While Killbus in public, Killbus was heavily mistaken for the dancer himself, leading the media to think that "Satoshi Kakizaki" had gone crazy. After Killbus' death, the current status of Kakizaki's public image was restored to normal.

Satoshi Kakizaki is portrayed by Gaku Shindo (進藤 学, Shindō Gaku).

Yui Mabuchi

Yui Mabuchi (馬渕 由衣, Mabuchi Yui) is a young elementary school teacher who is looking for Kamen Rider Cross-Z, because she has faint memories of what happened before Sento merged the two worlds, when she was captured by Faust and died as a result of their Lost Fullbottle experimentation. After Killbus began the process of destruction with the Pandora Box, she recovers all the memories of her alternate self and blames Ryūga and the other Kamen Riders for not saving her together with her students, who are still in comas due to the events of the old world where they were attacked by Faust's Guardians. After Killbus is defeated and her students recover with the power of the Genius Fullbottle, she forgives Ryūga and to others, helping him in the sale of Sento's experiments and starting a new relationship with him in the process.

Yui Mabuchi is portrayed by Mariya Nagao (永尾 まりや, Nagao Mariya).

Downfall

Downfall (ダウンフォール, Daunfōru) is an international radical terrorist organization that appear as the antagonists of Build New World: Kamen Rider Grease. Its members are actually those who had been experimented by the Nebula Gas and ex-Faust members from the old world; all aiming to exploit the Rider System and achieve world domination. They hack Japan's Guardians and Hard Guardians to use the androids as their weapons.

Using man-made Metal Bottles (メタルボトル, Metaru Botoru), they can transform into olive green-colored battle forms known as Phantom Crushers (ファントムクラッシャー, Fantomu Kurasshā); are armed with missile launchers, aerial capabilities, and the ability to disable Rider Systems with their right hand, which can absorb the Rider System users' Nebula Gas to lead them to lose the ability to transform.

Downfall is notable for being the first villain organization in the Kamen Rider series where the majority of its members are portrayed by foreigners.

Keiji Uraga

Keiji Uraga (浦賀 啓示, Uraga Keiji) is the leader of Downfall known for his face who is a mad scientist captivated by technological advancement driven by war. Like Yui Mabuchi, he has burn marks and his memories of the old world because he was a Lost Fullbottle test subject. He was originally one of Faust's scientists who studied the Last Pandora Panel White alongside Shinobu Katsuragi and Evolto, but died as a result of their Lost Fullbottle experimentation. He determined to obtain the Last Pandora Panel White and dominate the new world as revenge for the old world that did not acknowledge his brilliance as a scientist, and he found Phantom Liquid (ファントムリキッド, Fantomu Rikiddo), which is more powerful than Nebula Gas, before creating the Phantom Crushers using the liquid. He takes Shinobu's Build Driver and Sento's Hazard Trigger to become his own Build, which he calls Kamen Rider Metal Build (仮面ライダーメタルビルド, Kamen Raidā Metaru Birudo), to confront the Sawatari farmers. He is later defeated by Kazumi in the Grease Perfect Kingdom form.

As Metal Build, he resembles the original Build Hazard Form using a pair of Metal Tank Tank (メタルタンクタンク, Metaru Tanku Tanku) Fullbottles; hence his black colored eyes. Aside from retaining Build Hazard's abilities, his use of a similar Fullbottle pair negates the Hazard Trigger's side-effects. After he is weakened by Grease Blizzard, Metal Build absorbed the Last Pandora Panel White and merged with a Phantom Crusher to become Phantom Build (ファントムビルド, Fantomu Birudo); equipping him with the Phantom Crusher's armor, which allows him to use super speed, aerial combat, missile bombardments, and even a copy of the original Build's Drill Crusher.

Keiji Uraga is portrayed by Tamiyasu Cho (趙 珉和, Chō Tamiyasu).

Simon Marcus

Simon Marcus (サイモン・マーカス, Saimon Mākasu) is a high-ranking official of the Alliance of Nations who seeks to dominate the world in collaboration with Downfall. Like other Downfall members, he also transforms into a Phantom Crusher. He is later shot dead by Uraga, who no longer needs him.

Simon Marcus, who shares his name with a real life professional kickboxer, is portrayed by Michael Tomioka (マイケル富岡, Maikeru Tomioka).

References

1. The Kamen Rider Build Cho Zenshu book
2. "仮面ライダービルド 最終回を終えて ご視聴ありがとうございました" (in Japanese). Toei Company. 26 August 2018. Retrieved 2 September 2018.

External links

• Cast on TV Asahi