Break the Cutie/Warrior Cats

A better question would be, which "cutie" in this series hasn't been broken?

• Ashfur: Ashfur spends (apparently) a fairly good portion of the second and third series insane with jealousy over Squirrelflight, who will never love him back. This culminates in him trying to kill her, Hollyleaf, Jayfeather, and Lionblaze; however, this fails, as Squirrelflight reveals that they are not her kits. Finally, he is killed off by Hollyleaf when he threatens to reveal the secret.
• Blossomfall: Briarlight's sister, completely ignored by their mother after Briarlight's injury (see below) to the point where she joins the Dark Forest just so that she can be noticed for once.
• Bluestar: When Bluestar is a young apprentice, her mother, shortly after promising her kits that she would always be there for them, is killed in battle. When she and her sister become warriors, her sister becomes pregnant with the kit of one of Bluestar's enemies, and shortly after the birth, the sister is hit by a car, leaving Bluestar to essentially raise her enemy's son (as well as her nephew) more or less by herself. Later, Bluestar gets pregnant by a RiverClan cat, and she must give up her 3 kits to become deputy. One of the kits doesn't make the journey, and Bluestar must watch her two remaining kits grow up in another Clan without ever knowing that she's their mother. Near the end of her life, Bluestar loses three deputies in the span of about 6 months at best; her final deputy (before Firestar) tries to kill her, and this causes her to essentially go insane for the rest of her life.
• Briarlight: A cute, young she-cat, in the prime of her life, goes to help a Clan elder as a tree falls. The elder dies; Briarlight is permanently crippled, and learns shortly after that her chances of survival at all are slim.
• Brightheart: As an apprentice, Brightheart loses an eye and has an ear shredded. When she is finally rescued, everyone assumes she is dead. When it's revealed that she has survived, she gets the warrior name "Lostface". Even now, anyone who's never met her tends to be unsure of how to react, and it's been implied that in some places the skin hasn't even grown back yet, even though it's been several years.
• Cinderpelt: As an apprentice, Cinderpelt severely injures her back leg and walks with a limp for the rest of her life. She is later revealed to have a crush on Firestar, but she can never act on it because she is a medicine cat.
• Crookedstar: When Crookedstar was a kit named Stormkit, he was in an accident that resulted in his jaw becoming crooked. Shortly afterward, his mother starts hating him and even changes his name to Crookedkit, which later becomes Crookedjaw when he becomes a warrior. He makes a promise to a cat from the Dark Forest that he will always remain loyal to RiverClan, and as a result, slowly everyone he cares about is killed off, including his parents, his brother, his mate, and eventually all three of his daughters.
• Goosefeather: Comparatively minor, but he is essentially believed to be insane, but is generally completely right with all his prophecies. It's just that nobody will believe him...
• Graystripe: His first mate dies giving birth to his first two children. His oldest daughter dies in book 8; his oldest son leaves the Clans forever to live in the mountains. Later, he is taken away from the forest entirely, and it's only thanks to luck that he even manages to find the Clans again. When he finally returns, he is demoted to warrior, after having been deputy. Finally, one of his daughters, Briarlight, is permanently crippled as an apprentice.
• Hollyleaf: Hollyleaf is obsessed with the Warrior Code, desperately trying to follow it to the best extent she can. Both of her littermates are members of this prophecy that is supposed to be above the Warrior Code, and she spends most of her life trying to figure out how she fits into it. She later finds out that her parents are a WindClan warrior and the ThunderClan medicine cat, and she just can't handle this. She kills the only cat outside the family who knows the secret, and then tells the rest of the Clans. She then runs off into the tunnels, which collapse after her. However, she survives, as revealed in The Forgotten Warrior. However, she is then Killed Off for Real in The Last Hope.
• Honeyfern: Relatively minor one. Just after finding out that Berrynose truly does love her, she saves Briarkit from a poisonous snake and dies after being bitten.
• Leafpool: She briefly leaves her Clan and unintentionally winds up pregnant. By a WindClan cat. When she returns, she has to give up her kits (although, admittedly, is to her littermate) and watch them grow up without their knowing that she's their mother, including having one of her sons apprenticed to her to train to be a medicine cat. When they finally find out, her daughter tries to kill her, and then winds up telling all of the Clans the truth. Shortly afterward, Hollyleaf is trapped for about a year in the tunnels, while Leafpool is demoted to warrior for having broken the Warrior Code as well as the Medicine Cat Code, and is forbidden from practicing medicine anymore.
• Longtail (only after his Heel Face Turn ): Shortly after deciding to be nice, he is blinded by a rabbit. Yes, a rabbit, one of their prey animals! For the rest of his life, he is an elder, despite being just a little bit older than Firestar at the time. When it finally seems like he might be happy, he is killed in Fading Echoes while helping his friend Mousefur.
• Poppyfrost: As a young apprentice, she almost died of greencough. Shortly afterward (apparently), her only brother dies and one of her sisters is temporarily taken out of training because of an injured leg. Her only remaining sister dies soon after they become warriors, and her sister's former (almost) mate chooses her. Now, she is very happy about this, because she has been in love with this tom since before her sister's death, but she cannot enjoy it because she thinks that he doesn't truly love her. It takes a message from StarClan to get the poor she-cat to believe that her sister doesn't hate her!
• Spottedleaf: She's killed off less than halfway through the first book, for StarClan's sake! Also, she's in love with Firestar (at the time known as Firepaw) but can't act on it because she's a medicine cat.
• Tawnypelt: She is the oldest daughter of Tigerstar, for one thing. She is so tormented living in ThunderClan that one day she just moves into her father's Clan. Shortly afterward, her father dies. Also, in series 3, she has to temporarily leave ShadowClan, with her young apprentice kittens, because of Sol's presence.
• Thrushpelt: Another minor one - he goes throughout life in love with a much younger she-cat who doesn't love him back, and pretends to be the father of her kits so she won't get into trouble. She never tells him the truth, and he is dead by the time Bluestar is leader.
• Yellowfang: Yellowfang has kits, even though she is a medicine cat. Only one kit, Brokenstar, manages to survive birth. Yellowfang must then give up her remaining kit to a queen who refuses to love him. Yellowfang now has to watch her son grow up. Brokenstar eventually kills his father and kicks his mother (though he doesn't know it) out of ShadowClan. Finally, Yellowfang is forced to kill Brokenstar in order to save her new Clan.