Kingdom Hearts/WMG/Confirmed

These are Wild Mass Guesses for the series Kingdom Hearts which have been confirmed by the games or by Word of God. If a WMG on one of the open pages is confirmed, please move it here.

The Possibility of other Key-Weaponry...

Why not? Keyblades could just be the most common form, or maybe their default form, there might be some wielder/master out there who wields a Keyspear, or a keybow. Maybe 'Keyblades' take the form of what the wielder is best at. Just a thought...

• Confirmed by the Lingering Sentiment and No Heart battles in the Final Mixes. Keyblades can transform into bows, whips, cannons, wings, skateboards, wings, drills, claws, shields, and leg guards.

Terra is Xehanort, Aqua becomes the sentience that chooses the Keyblade wielder, and Ven is Sora's spare heart.

It addresses all the WMG and unexplained plot elements of the first few games, as well as Terra's noted similarity to Xehanort; Xenmas's addressing of Aqua's armor, and some of the cryptic comments he made are also explained by this. This could also explain why it went from MULTIPLE keyblades (Birth By Sleep) to one, much more powerful, form shifting Ascended/Sentient Weapon.

• Confirmed on Terra is Xehanort.
• The spare heart thing may or may not be true. At the very least, Sora has Ven's heart inside of him.

The plot of the next game featuring Sora will center around fixing Birth by Sleep's inevitable Downer Ending.

Just listen to Ansem's lines in the Jump Festa '10 trailer. Now, this does not mean he will go back in time and make everything okay again. Rather, he will undo the bad things that happened. For example, if Terra does becomes Xehanort, Sora will try (keyword "try") to return him to his previous form. If Ven's heart is taken, Sora will try to get it back. Maybe he'll even make Pete a superhero again.

• {{[spoiler|Pretty much confirmed but extended to 358/2 's ending, and the end of Kingdom Hearts II's prolouge. No word on Pete though.}}

Xemnas knew he was Terra.

And that why Xemnas came to see his "Friend" in Final Mix+ .

• It'd make sense, at least at a subconscious level. After all, Xehanort is the merger of Master Xehanort's heart and Terra's body and heart, the latter of which is Fighting From the Inside. Throw in the Laser-Guided Amnesia from Terra forcing Xehanort to lock away his heart, and this theory really doesn't seem that farfetched. After all, Xehanort has the hearts of Terra, MX, and (if Terra's cryptic words are anything to go by) Master Eraqus, so who's to say that his already fragmented memories aren't having adverse and unexpected effects?
  • To add to the above: Xemnas was slowly regaining his memories as the years went on. That's why he recognized Aqua. He remembers bits and pieces of his former life. That's the real reason he wanted to merge with Kingdom Hearts. He wanted to use its power to restore his lost memories and be whole again.
  • Also adding: As said, Xehanort is the merger of Master Xehanort's heart and Terra's body and heart. Nobodies are formed from the body of one who has lost their heart. When you take out his heart(s), what's left? Terra's body. Xemnas is the closest out of all of Xehanort's incarnations to being purely Terra, so no wonder he remembers being him!
    • I must become one with Kingdom Hearts. I will become a higher existence. All of my true ambitions begin there.
    • Xemnas watched a comatose Roxas and thought to himself, "So you are asleep again..." referring to Ventus. He totally knew.
    • Judging by the Ultimania, Confirmed!!

Axel's Other's name, Lea, is actually correct in the English phonetic form, and is meant to be part of the AxelRoxasXion Power Trio

• Because the name "Lee" means a meadow or a plain, like land . Therefore, when added with the unscrambled anagram of Roxas's name with the 'x' removed, Sora, and the 'Shio' part of the Japanese rendering of Xion, Tide, we have another Sea, Sky, Land Power Trio.

Ven's heart is bound to/merged with Sora's heart.

• Sora is the Chosen One/whatever you want to call the one destined to open the Door to Light and banish the darkness, and Ven knows this. He knew when he met Sora, and he wanted to make sure Sora didn't die or anything, so Ven bound his own heart to Sora's. Then something went wrong (at the end of the game, maybe?) and now Ven is the other side of Sora's heart, from which Roxas takes his appearance. OR, alternatively, Ven's heart exists within Sora, much like how he had Kairi's heart within him in the first game. It was released when Sora became a Heartless, and when Roxas was born, his... essence and Ven's heart were crossed, hence why Roxas looks almost exactly like Ven.
  • Confirmed! After defeating Vanitas, his Enemy Without, during a Battle in the Center of the Mind, Ven falls into a coma, but his heart goes on to meet Sora. The young Sora takes Ven's heart and integrates it into himself.

Unarmed combat

At some point in the series, someone (my bet's on either Sora or Kairi) is going to lose their keyblade (again, in Sora's case). But as Sora says in the first game, "I don't need a weapon! My friends are my power!" Only this time, it'll be true - and a battle will be fought without the keyblade while still being effective, either barehanded or with another weapon. Sora and Kairi seem to be the most obvious choices - out of the wielders we've seen, Sora's been the most attached to the Power of Friendship, whereas Kairi, being a Princess of Heart, could very well weaponize her inner light to the point of not needing an actual keyblade. For extra points, combine this with any of the Vanitas-as-Big Bad theories above, especially ones that involve either him forging the Chi-Blade or just Sora losing his keyblade for whatever reason.

• Confirmed by the world Hollow Bastion in Re:coded, wherein Maleficent squashed Data-Sora's Keyblade and Donald and Goofy run through the entire world as his weapons.

There is a third, as yet unknown, group of enemies, to oppose the Heartless and Nobodies.

The Kingdom Hearts series loves to make references to trinities: Sora's ultimate team-up attack, the floor design in one of the rooms in the mansion outside of Twilight Town, even the number of members in the party. However, as it stands so far, there are only 2 groups of enemies: the Heartless (represented by the black heart wrapped in thorns) and the Nobodies (represented by the half cross, half inverted heart symbol... thing), which doesn't seem to match the pattern... unless there is a third group, which is, as yet, unknown. They already have their own symbol, as shown in the mansion outside of Twilight Town: the crown. Seeing as the Heartless are darkness, and Nobodies seem to fall in the middle of the Light/Dark spectrum, the logical assumption is that this third group is symbolic of light. One scenario is that, when a Heartless is created, the "goodness" that was lost from the heart to create the heartless goes off and becomes a new being, much like how the Nobodies are created from the now empty shell of people that succumbed to the darkness once their heart has left them.

• Of course, we could interpret the trinity to be three opposed forces: the Nobodies, the Heartless, and the protagonists.
• It's rumored that a such a third force will appear in KH3. The rumored name for these enemies is either Soulless or Dis-Souls.
  • At the Alter of Naught, Mickey arguably says outright that the third side is Light -- "You no longer belong in the darkness, Riku." Thus, the trinity is darkness, light, and nothingness, and is also suggested in the final fight with Xehanort, where he mentions that light and dark are eternal, and so too is nothingness. If so, then the third enemy will be people who lost their hearts to Light itself. This could go one of two ways. If "light" and "darkness" map straight to "good" and "evil", then these would simply be beings of pure good; however, Riku's situation implies otherwise. Thus, these would be beings of pure Light -- which may imply, for instance, Knight Templars.
    • That would explain the knight-like appearance of Terra, Aqua, and Ven.
• There should be a group of beings composed of pure fear, and known as the Spineless. :)
  • Or, alternatively, the Gutless...
• Or perhaps the third group consists of people whose Nobodies and Heartless were destroyed and became whole again.
• This is confirmed - they're called Unversed, and they appear in Kingdom Hearts: Birth By Sleep.

We haven't seen the last of Vanitas.

C'mon, he's practically Sora's evil twin. He gets multiple boss fights including the secret boss fight, which is more than what Xehanort got even if you count Terranort. He comes closer than anyone else to forging the ultimate keyblade, and despite Ven's best efforts, some part of him may still be in either his and/or Sora's heart. Nomura seems to love this guy, and with Sora running off on his own to "reconnect" everything, it'd seem like an interesting concept to have some part of him that he may not want to reconnect. Somehow, in some way, he'll be back.

• • My theory is Vanitas is connected to Sora's Anti-Form. Think about it, when Sora became a Heartless, he only had enough darkness in his heart to become a Shadow, the weakest mook around. Where did he get the darkness for the whirling dervish of death that is the Anti-Form? Methinks, at the very least, in KHIII Anti-From will be looking a lot Vanitus and Riku's dark mode, possibly even aquiring Vanitas's Keyblade
  • I was kind of thinking the same thing. It'd make sense, seeing as Sora has Ven's heart, thus meaning that Vanitas could still be lurking in some dark corner. I mean, Xehanort's Heartless still has a small part of himself lodged into Riku's heart, so why not Vanitas? It'd make a pretty stellar twist, especially considering that Sora has already ventured towards becoming a Heartless again thanks to Anti-Form.
  • Let's take that a step further; Nomura is obviously building up Sora's quest to bring back everyone he can, including Xion/Roxas/Naminé/Aqua/Ven/Terra/etc etc. Presumably this would involve getting them their own hearts/souls/bodies/whatever they're missing, possibly by invoking some use of Kingdom Hearts. But Ven and possibly Vanitas are in Sora's heart; suppose breaking the links between them results in Vanitas hijacking the combined darkness of Sora/Roxas/Xion and adding it to his own darkness? Now we have a setup where Sora's accidentally created a monster even worse than Xehanort and with Sora's heart completely purged of darkness, fighting him will inevitably result in the recreation of the χ-blade.
• Confirmed, he will appear in Kingdom Hearts 3D.

Xemnas/Xehanort is the most incredible schemer in history.

• The entire, and I mean ENTIRE, series from BBS to KHII has been one massive Evil Plan engineered by Xehanort. Think about it, no matter what happens, he always manages to come back and screw the worlds over even worse than before. He started in BBS and when he became a Nobody he continued his mission as Xemnas. Seriously, though, what if he actually wanted to be destroyed as Xemnas so he could finally rejoin with his heart and be a complete person once more and gain the power of the heart that he's always wanted? What if by defeating him Sora unwittingly gave him what he always wanted? Now he can return. Nomura stated that when a Heartless is destroyed, it enters a limbo and waits for the Nobody to die too. What if this limbo is near or even is Kingdom Hearts itself? He can now practically touch Kingdom Hearts and it's all Sora's fault!
  • Well, that's Kingdom Hearts III, isn't it?
  • You're close, but it's not Xemnanort who is manipulating everyone, but the Moogles. They've been selling weaponry to both sides of the conflict for years.
  • Confirmed. Through the power of time travel, everything that's happened from when Xehanort was a teenager up to 3D has gone according to his plan.

Nobodies are something more than bodies.

Contrary to what Yen Sid says, the more advanced Nobodies do indeed seem to have emotions, hopes, dreams, and all the basics of a true person; indeed, the biggest irony in the game that they wouldn't want them so much if they didn't already have them. One possibility is that the creation of a Heartless is more complex than just heart/body separation; pieces of each are left in the other. Another is that the separate pieces still share the same soul, which runs both at once.

• Yen Sid also mentions that they're "spirits" of some form. Even if they are simply hollow, animated husks, perhaps the emotional memory is imprinted somewhere in the Nobody and causes them to miss the sense of "feeling" things.
• Another possibility is the concept of the philosophical zombie. Essentially, a P-Zombie is a theoretical state in which there is no consciousness, no self, but the P-Zombie acts indistinguishable from something that does have a self.
• My theory about it has always been that this has something to do with translations and the fact that Japanese has different words that generally do get glossed as "heart", but have distinct meanings. "Heartless" actually lack the mind/soul componenet and are driven by basic instinct (one could say the Id, I suppose). Really basic nobodies- the dusks and so forth- are really simply the bodies, but the really really strong-heart/souled people had their mind/sould component cling to their body, hence why they got to retain their memories and personalities; however, they lack the ability to feel anything viscerally. This also accounts for the apparent emotions they have- they can have intellectual opinons on matters, including intellecutal attachments or repulsions to other individuals. They would also be able to make moral judgements, perhaps, along with the memories of what friendship should be like, explaining Axel's defection from the Organization to help Roxas. Note that this theory does not apply to Roxas, since I agree with other WMGs on the page that he possesses at least some of Ventus' heart, nor to Xion, since she is not a proper nobody, but constructed from Sora's memories/some part of Kairi's heart that remained in him or the part of his heart that held his emotions toward Kairi. Hence, they both have proper emotions.
  • Confirmed. They have souls and the beginnings of hearts as well.

Nobodies really can feel emotions.

However, it takes extraordinary circumstances for them to really feel something. My guess is that Nobodies usually feel, at best, some sort of half-empty feelings but when they feel a real emotion, it is a pretty big deal for them. Example: in Re: Chain of Memories, after Axel frees Naminé and tells them to put on a good show for him, he stops, puts his hand to his heart, and muses to himself "Wait. I'm enjoying this." The fact that Sora's crew caused him to feel a real emotion is a big thing for him. Some other emotions may be real; such as Vexen's fear of death, but it's hard to be sure what they fake, and what they really feel. Yen Sid was right when he said that Nobodies can put on an act of having emotions; but he was wrong in saying that they can't feel.

• • Confirmed. Xemnas reveals that Nobodies can grow hearts, and thus feel real emotions.

Axel is dead.

Because Square Enix has shown no mercy over permanently killing off popular characters before.

• It depends on the game. Compare Final Fantasy II to Final Fantasy IV, for instance.
• Tidus. 'knuff said.
• Confirmed... kind of. Axel seems to be gone, but Lea's around, and they are nearly identical.

Xehanort will return.

Nomura has confirmed that when a Heartless and its Nobody are defeated, they are reunited and reborn. Both Xehanort's Heartless and Nobody have been defeated, meaning that Xehanort has been reborn and is lurking somewhere out there.

• Yes, but probably as a baby.
  • What.
• Actually as a complete being as Xemnas and Ansem are destroyed so if both their seperated existences are destroyed, the former original form will rebirth.
• Xehanort's Heartless was not completely destroyed by Kingdom Hearts blowing up, as he has tied his existence to Riku's heart. Riku would have to become a Heartless and be killed first.
• Confirmed. He and several other of his incarnations is alive and well as of KH3D.

Roxas can still feel emotions.

In 358/2 Days, during Roxas' mission with Xigbar, Roxas keeps fretting about Castle Oblivion, worried that Axel's dead. Xigbar tells him that the quicker they get on with the mission, the sooner Roxas will find out the truth. Roxas replies "I know". But he still worries, even though he knows Xigbar is right. Remember what Axel said to Roxas about people who have hearts? He said that their emotions are irrational, that people with hearts can't help but feel a certain way. Not only is Roxas the only Nobody who gives a damn if one of his comrades dies, he worries about Axel irrationally and despite himself.

Roxas is a unique Nobody; his heart's still around in the form of Sora. It's possible that his connection to Sora gives Roxas a rudimentary form of a heart.

Definitely possible. Roxas shows more signs of emotions than every other Nobody put together, doubly so due to him not having memories and so the whole 'Faking it from memory' thing doesn't apply. In addition, there is Ven's heart to consider too.

• Confirmed. Roxas gives Sora his memories, and afterwards, Sora comments about all the emotions Roxas felt.

Nobodies base their personalities around the memories of their old self.

Which is the reason, why Roxas started out as a zombie, as he puts it himself in 358/2, and ended up developing a completly different personality from Sora, except for a few treads like hard-headedness and loyality to his friends.

• Confirmed.

Xion will at one point be brought back…

As an antagonist boss fight while dressed suspiciously like V-13 from BlazBlue. She will be emotionless and robotic like around everyone else, but when Sora comes up she will be a creepy, bubbly, evil girl.

• Why? Xion willing to commit suicide by best friend to save Sora when she had never even met him. Why would she suddenly try to attack him when he is trying to rescue her and her friends? as seen in Birth By Sleep.
• The Jump Festa trailer seems to confirm that Xion will indeed be back, and considering she's seen pointing her keyblade at Roxas, she might even be an antagonist.
• Confirmed on Xion returning. She briefly appears in The World That Never Was in KH3D.

Miscellanious things that will happen in KHIII

• Lea will aid Sora and co, having revived after Axel and Lea's Heartless were both defeated.
  • Confirmed, except that It occurs in KH3D instead.

Among the people Sora is connected to that he saves in the upcoming games, Axel will not be one of them.

In the secret movie for re:coded, the people Sora will save all look up to the sky and whisper his name. When it gets to Roxas, Xion, and Axel on the clocktower, only Roxas and Xion say Sora's name, while Axel only looks up. In Birth By Sleep, Lea, Axel's Pre-nobody form, says that he likes to make friends and have them remember his name because in people's memories, he will live on forever. These moments are symbolic, and hint to the fact that Axel will not come back, but his memory will live on.

• • Lea, however, might make an appearance.
  • The Jump Festa trailer confirmed that Lea will be back.
• Confirmed. Lea's back and does not need saving. Axel's gone, but they're pretty much the same person anyway.

Xemnas's and Xehanort's Heartless's obsession with Kingdom Hearts comes from Master Xehanort

• (Not OP) This was pretty much confirmed by Word of God. Additionally, Xemas's obsession with the letter X comes from MX's obsession with the χ-blade.
• Confirmed.

Xemnas's and Xehanort's Heartless's obsession with Kingdom Hearts comes from Master Xehanort's obsession with the X-Blade

The X-Blade is supposedly equal in power to Kingdom Hearts itself, which is the entire basis for this WMG.

• Confirmed.

Master Xehanort engineered the organization so he would have extra bodies without hearts to transfer his into.

• Based on the english translation of Birth By Sleep's storyline and OMG SECRET ending, Master Xehanort promised Braig he would make him a keyblade wielder. In the secret ending, he refers to Terra as only one of the many roads he might take to reach his goal. Logically, Braig doesn't have a strong enough heart to have a keyblade, so he could only get one by Xehanort transfering his heart into his body, like he did with Terra. It explains why certain organizations members have the Gold eyes and pointy ears, as they're the ones who have enough darkness within for Xehanort to possess them.
  • HOLY CRAP! This is more or less CONFIRMED!

The X in the X-blade and the X's of Organization XII are connected.

• Confirmed by Word of God. Xemnas is in charge of organization XIII and names all the new members and his memories of his life as Master Xehanort lead him to the same obsessions as the original.

Dreams will play a major plot point in a future installment

Whether it's a spinoff or a canon game, they will. It'll be something like, dreams are projections of our heart's strongest feelings. When our hearts are filled with joy, we have good dreams, and when they are in distress, they are temporarily filled with darkness, and nightmares occur.

• Confirmed. KH3D is set in the Realm of Dreams.

Kingdom Hearts 3D is partly or entirely Sora and Riku's Mastery Exam.

The game appears to involve both Riku and Sora and the mastery exam is the only loose end besides Mickey's adventures before the final dance with Xehanort.

• Confirmed.

Mysterious Figure's Identity (Birth by Sleep)

Long List Ahoy

Facts about Mysterious Figure:

• Location - Land of Departure
• Weapon - "No Name", two Etheral Blades-like Keyblade that resembles high-tech/magitek swords.
  • Weapon (Fused Form) - Similar to a quarterstaff
• Size - Roughly Terra's height
• Build - Muscular, possibly masculine
• Clothes - Similar to Organization XIII black coats.

Hypothetical Choices

• Master Xehanort
• Terranort
• Xemnas
• Ansem the Wise
• The Teacher of Master Eraqus and Master Xehanort
• Master Eraqus' Nobody
• Master Yen Sid
• New Person
• Master Xehanort's Nobody

Status Master Xehanort:

• As of the end of Birth by Sleep is fused together with Terra. Combat-style is different.
• Eligability: Disproven

Terranort:

• As of the end of Birth by Sleep is memoryless in Radient Garden. Cannot access Keyblades due to lack of knowledge that he can use them. Combat-style is different. Can be fought as Terra.
• Eligability: Disproven

Xemnas

• Does not exist yet. Combat-style is different.
• Eligability: Disproven

Ansem the Wise

• Avaliability is viable but will be betrayed anywhere between a couple months to a year later. Combat-style uncertain. Build is similar (see DiZ) and weapons would make a decent parallel to Xemnas's Etheral Blades as Xemnas (as Terranort) stole everything else that used to be Ansem's.
• Eligability: Possible

The Teacher of Master Eraqus and Master Xehanort

• Little knowledge is known. Possibly deceased but considering the weirdness that is the universe's treatment of the soul this may not matter.
• Eligability: Possible

Master Eraqus' Nobody

• Physical build is simiar, highly experienced Keyblade master, could be manifest already and wants to test his pupils. Where the keyblades came from is unknown.
• Eligability: Possible

Master Yen Sid

• Alive and location not confirmed during the events towards the end. Gave his Keyblade to his successor King Mickey. Build similar.
• Eligability: Possible

New Person

• No knowledge avaliable.
• Eligability: Unconfirmed

Master Xehanort's Nobody

• Eligibility: Likely
• Nobodies are specifically created from the disjoining of a heart from its body. Sora creates Roxas and Namine by releasing his heart from his body, the same way Xehanort releases his heart to possess Terra. Xehanort's body dissapates, the same way Sora's did. From this, we know that there is Xehanort Nobody out there somewhere, with all of Master Xehanort's memories.

Result Possible Candidates for "Mysterious Figure" are Ansem the Wise, the Teacher of Master Eraqus and Master Xehanort, Master Eraqus' Nobody, Master Yen Sid, and a new person.

• I'm gonna nitpick, but his weapons aren't necessarily "No Name"; the No Name Keyblade is simply based on those swords. Donald's Skysplitter-based wand is called Centurion, not Skysplitter.
  • I understand that but considering that we don't know much (if anything) about the Mysterious Figure, the name of the Keyblades (Heroes' or MF's) very well may have a spoileriffic name far beyond any typical preview would allow. Or it may literally be the name as a possible allusion to Nobodies.
• I think its a bit hasty to throw out characters just because they don't exist at that time. Time travel could be involved. It happened in Kingdom Hearts II with Pete so its likely someone else can do it too. Maybe its the new Xehanort formed after Ansem and Xemnas got the axe.
  • Perhaps, but the Bonus Bosses in previous KH games have a track record of factoring into the plot of the rest of the series. Xemnas showed up as "the Enigmatic Man" and Terra's Lingering Sentiment made his debut in the Final Mixes of KH 1/2 respectively.
• Confirmed for Master Xehanort, Jossed for all the others.

Braig will be Master Xehanort's next host

So, Sora apparently has to save Terra. The only way to do this is to drive Master Xehanort out of Terra's body. However, Master Xehanort's body disappeared after he put his heart in Terra, so he'll neeed a new one. Now, if Braig's heartless was destroyed before Sora defeated Xigbar, then Braig could be back. Master Xehanort's heart will choose him as a host, and the player will be able to lay the beat down on the two biggest jerks in the series at the same time. Whether Braig lets Master Xehanort possess him willingly or not is another question altogether.

• • Maybe, but slightly unlikely. The ending re:Coded implies that due to the deaths of Xehanort's Heartless and Nobody in that order, Xehanort is already back as his original self (somehow), although its unknown if it's Grandpa!Xehanort or Teen!Xehanort as briefly seen in Birth by Sleep. He could still try to attempt Grand Theft Me if his original body (or more specifically, his old age if he's not a teenager once more) proves to be a liability again.
  • Confirmed in Dream Drop Distance, as he reveals he's ALREADY been partially Xehanort for a while now. In fact, this was the reason he formed Organization XIII in the first place -- to gather together 12 extra hosts, and use Kingdom Hearts to make them empty vessels for his heart and mind.

Birth By Sleep: Final Mix will include a fight against Xehanort's Armor.

And further, it will take place on Destiny Islands. We know that Xehanort used to have armor like the other keyblade masters, but discarded it when he fell into darkness, and also that he was originally from DI. In normal BBS, Destiny Islands is still accessible from the world map even though you can't land on it and nothing else plot-related happens there after the first visit. In the previous games you could never access it. The fact that it's still on the map just screams "Chekhov's Gun".

• Partially confirmed. There is a new boss fight called "No Heart" in the Mirage Arena with what looks like a cleaned-up version of Xemnas' armor from KH2, wielding Master Xehanort's keyblade. It doesn't look like the fight will take place on Destiny Islands, though.

Heart fragments can grow into complete hearts.

At the beginning of Days, Roxas acts zombie-like and is really zoned out. Throughout the game, he connects with Axel and Xion and becomes more normal. Xion also goes from zoning to acting like a normal person, and Axel seems to become friendlier. It is heavily implied throughout Days that Roxas, Xion, and Axel develop emotions. If Ven's heart went to Roxas when Sora stabbed himself (I have heard that Nomura confirmed this, but I have not seen the confirmation myself), then Ven's heart may have been able to help Roxas keep any fragments of heart that he kept from Sora from vanishing, in the same way that Sora stopped Ven's heart from vanishing.

I also believe that Roxas's heart may have been able to influence Xion's and Axel's (supposedly nonexistent) hearts. In KH1, Kairi was able to use her heart to revive Sora. My theory is that hearts can reach out and facilitate the growth of fragments of heart, usually through friendship. I think that human-looking Nobodies like Organization XIII retain their human form because they have fragments of hearts within them. It would explain why only people with strong hearts have human Nobodies, since people with strong hearts would be most likely to hold onto heart fragments. According to this theory, Axel has heart fragments, which grew into a fledgling heart through his interaction with Roxas and Xion. Roxas's heart grew through the same process.

• Confirmed. Xemnas reveals in KH3D that Nobodies can grow hearts.