Anime often features radical transformations. Characters sprout auras, change hair colors, increase their muscle mass, or come closer to reaching a divine persona that leaves the very earth shaking beneath them. Some of these transformations are truly monstrous, grotesque transformations that leave audiences feeling more than a little uncomfortable.
While it's not unusual for antagonists or villains to undergo nightmarish transformations, heroes transforming so grotesquely is at once less common and more horrific. Here are eight of the grossest hero transformations.
Akira Fudo (Devilman)
No matter what iteration of Devilman you watch or read, one thing remains the same: Akira gets possessed by the demon Amon and becomes the stuff of nightmares. Even if the old '70s Devilman anime seems tame by modern standards, he still becomes a monster that kills other monsters. The presence of Devilman is terrifying enough to elicit madness and paranoia in society. Even if the real monsters weren't people in Devilman, Akira's fusion with Amon is horrific. Arguably this is most obvious in the OVA, Amon: The Apocalypse of Devilman, where Akira gives into Amon's influence, and the titular demon gores and devours a child member of the Devilman Corps, Yumi.
Kyo Sohma (Fruits Basket)
Kyo is one of the many members of the Sohma family cursed to transform into an animal when hugged by a member of the opposite sex. Kyo turns into a Cat, which at first seems like a harmless enough transformation. However, Kyo's second transformation, triggered when the beads around his wrist are removed, is far more grotesque. A manifestation of ugliness and self-loathing, Kyo's second form is enough to drive the ordinarily unphased Tohru Honda into a historical fit of terror. If not for Tohru's love, it's possible transforming into this form might've left Kyo forever a lonely, self-loathing shell.
Armin Arlert (Attack on Titan)
Multiple individuals in Attack on Titan can transform into the titular Titans -- specifically, a select group known as the Nine Titans, eaching possessing unique powers. While Eren Yaeger has made it his duty in life to transform into each and every Titan by collecting the power of three of the Nine into his being, Armin Arlert might have the most grotesque transformation of all.
Armin can transform into the skinless Colossal Titan, following the demise of the previous Colossal Titan, Bertolt Hoover. Armin's Colossal Titan is gaunter than the previous iteration, with several of his bones sticking out through his sinew. This sluggish transformation will eventually kill Armin, thanks to the Curse of Ymir.
Shinichi Izumi (Parasyte)
Parasyte is a body horror anime about alien entities infesting and mutating the flesh of their hosts, reminiscent of both Go Nagai's Devilman and John Carpenter's The Thing. However, Shinichi had the "good fortune" of having his alien parasite, Migi, only infest part of his body after overtaking his hand. The two form a symbiotic partnership, fighting off other Parasites by creating blades and weapons from his flesh.
Later on, Migi spreads throughout Shinichi's body, allowing him to basically use his whole body as a weapon of destruction. He can twist and calcify his flesh, sprout new limbs and even regenerate. Of course, this power comes with the drawback that Migi has replaced his arm with a weird eyed, mouthed thing that can hop off his arm and run around his room like a dog if he so chooses.
Chise (Saikano)
A young innocent girl is turned into the ultimate weapon. While Chise doesn't sprout new organs or change her exterior, the monstrous transformation Chise undergoes is one that lingers below the skin. Her insides are eaten away by machine parts to fight a brutal, grotesque war that does not make any sense to her.
The monstrous horror of Saikano is one of existential dread, with her body continually altering until we see the full extend of what the government has done to her when we see her skin literally peel away to reveal her organs have been eaten-up by mechanics. She loses her ability to feel, taste, touch, generate body heat -- resulting in a genuinely disturbing body horror anime unlike any other.
Ken Kaneki (Tokyo Ghoul)
Ken, following a romantic encounter from Hell, becomes a monstrous, flesh-devouring ghoul. However, while the change in eye and hair color aren't extraordinary transformations, his inner appetite for human flesh is quite the monstrous new manifestation of his abilities. If that isn't monstrous enough, Ken has multiple other forms, within his body being covered in armor-like scales. The release of kagune -- tendril-like organs used to defend and fight -- are also pretty gross.
Ken's most horrendous transformation, though, comes following being transformed into the Dragon, a colossal kaiju-esque kagune that ripped Tokyo apart. The only salvation Ken received was when he was physically ripped from his own growths. That's a pretty brutal form of surgery there.
Rei Ayanami (End of Evangelion)
Rei Ayanami's transformation in End of Evangelion, where she merges with the Angels Lilith and Adam, does not on paper appear too scary. After all, it's just her only planet-sized and naked. What makes Giant Naked Rei so grotesque is how uncanny she appears throughout the whole of her transformation.
While her will is enacted in Instrumentality to Shinji, with her talking and communicating with him clearly, her body is this big doll-like structure that elicits an aura of almost Lovecraftian terror. It's the epitome of the Uncanny Valley, being so close to human yet not. Her actions during Instrumentality are enough to drive mankind into madness. By the end, all that's left of Rei's body is a corpse that cannot rot, crumbling away, staring at the re-birthed population.
Alucard (Hellsing)
Alucard is literally Dracula, only a hero by virtue of declaring loyalty to Sir Integra Hellsing. As one of the most notorious vampires in history, Alucard has no shortage of monstrous abilities. The worst among them is when he unleashes his true power. He sprouts familiars from his flesh, be they demonic hounds from Hell, the souls of those he has slain in life, or any assortment of tentacles, eyeballs, or fangs.
What makes Alucard so fearsome and grotesque is his formlessness when transformed. Anything can seemingly sprout from his body while transformed, all of which can twist the very reality around an adversary, turning the world into an extension of Alucard's bloody flesh. Unlike others on this list, Alucard is already a monster to begin with, but it's only on certain occasions he transforms into his true monstrousness.