The Mind Is A Plaything Of The Body / Anime & Manga

• The 100 Girlfriends Who Really, Really, Really, Really, Really Love You: Kusuri Yakusen's failed "Immortality Drug" causes those who have taken it (Kusuri herself, her parents, and her grandmother Yaku) to have the bodies of eight year-olds. However, of the family only Kusuri herself is prone to acting like an eight year-old. There is a noticeable contrast whenever she temporarily reverts to her 18 year-old self with her "Negation Drug", such as being embarrassed about playing with toys when child Kusuri had been gleefully doing so throughout the rest of the chapter. According to Yaku, this is because Kusuri took the drug while her brain was still developing, so she's more susceptible to her mental age changing than the adults. Whether this is true is unclear, as Rentarou doesn't completely buy this explanation.
• Ayakashi Triangle:
  • After being turned into a girl, Matsuri's overall personality remains mostly masculine, but he occasionally has exaggeratedly feminine mannerisms. Shirogane insists the spell he put on Matsuri only affects his physical body, but Reo wonders aloud if an anatomically-female body itself is making his spirit trend toward the feminine over time. Whatever effect seems quite minor, but it becomes a recurring fear of Suzu's that Matsuri may become "a girl in heart and soul"—because she (initially) found Matsuri's male form more attractive and assumes that would make Matsuri fall for a guy instead of her.
  • Suzu can temporarily absorb ayakashi to use their powers, but this also affects her personality. Absorbing Shirogane made her a Cat Girl who fought more aggressively, licked herself, ran on all fours, carried objects in her mouth, and was way physical affection to Matsuri.
    Matsuri: What's gotten into you?! Stop licking meee!
    Kanade: She's in heat...
• Claymore: When a Claymore over uses their powers and is transformed into an Awakened being, their personalities are changed, meaning a Claymore that would once thought they would have killed themselves if they transformed will no longer even consider doing that.
• Bagi, the Monster of Mighty Nature plays this for tragedy. Bagi starts out as a Funny Animal, but turns more and more feral as time passes.
• Makaku in Battle Angel Alita explicitly references this idea when he becomes quite intelligent after losing his initial large cyborg body and is reduced to an ambulatory head.
• Mai Natsume of BlazBlue: Remix Heart was magically transformed into a girl, and gradually changes to naturally act feminine, stop seeing girls sexually, fall in love with a boy, and generally think of herself as being a girl rather than a boy in a girl's body. However, it's ambiguous how of this was the direct result of her transformation as opposed to her constructing a feminine identity as a disguise and liking it more than her original.
• Inverted in one chapter of Cat-Eyed Boy. A Mad Scientist attempts brain transplants... but later discovers they can't be successfully performed, as the new mind housed in the body will eventually force its new body to match the one it was originally housed in.
• In Darker than Black, Body Snatcher Mao needs Phlebotinum to maintain a human level of consciousness; without it, his personality is eventually overridden by the instincts of the cat whose body he inhabits.
• Digimon:
  • As a general rule, Digimon become more brutish with stronger forms unless they cross the Bishōnen Line, while how much their actual personality changes varies by how much personality they have to begin with.
  • When Takuya first attains his Vritramon/Burning Greymon form in Digimon Frontier, he flips out and nearly takes Tomoki's head off, until one of Tomoki's tears falls into Takuya's eye, causing him to regain his sanity. While all of them had trouble controlling themselves in their beast transformations at first, only Takuya lost complete control. Except Izumi, for some reason; she attributes her ease of control to being a girl, but says it so obnoxiously that the boys feel ready to throw up. Izumi happens to also have a "beast" transformation that's basically still human in all but the most minor aspects and in fact qualifies as an in-universe case of Ms. Fanservice. Koichi also had no trouble, but he's the group's Sixth Ranger, had previous experience using it while still Brainwashed and Crazy, and by the time he joined up the beast transformations were So Last Season.
• Dragon Ball:
  • In Dragon Ball, Saiyans who still have their tails turn into gigantic weremonkeys when exposed to the light of the full moon (or a similar enough substitute), becoming savage and violent no matter how docile they are in their humanlike form. Only Saiyans who have had the proper training can stay in control while transformed. Likewise, there's the Super Saiyan transformations, which turn even the nicest Saiyans (like Goku and Gohan) into the ruthless, cold-hearted warriors Saiyans are known as throughout the universe, with no desire other than to exact painful revenge on whoever angered them enough to trigger the transformation. Played With in that those who learn Super Saiyan eventually do learn to control the transformation and maintain a calm demeanor; with Goten and Trunks maintaining theirs when they’re exposed to their family.
  • In Dragon Ball Super, we get the villain Goku Black, who looks identical to Goku, but makes an indication early on that he originally did not have that appearance. Then we learn the reason for it is that he's actually a Supreme Kai named Zamasu who, out of envy and spite, stole the body of an alternate version of Goku. The curious thing about it is that his personality seems to have been altered slightly by this and he's taken on some of Goku's personality traits, particularly his desire for battle, and need to be challenged and grow stronger. Then after Black actually fights Goku even his speech pattern slowly grows more and more like Goku's. He also starts using some of Goku's fighting stances and techniques, although those are in part deliberate imitations. His penchant for meal metaphors to describe his opponents may also be an artifact of the real Goku being Obsessed with Food.
• Zigzagged in Durarara!!. When Celty witnesses Kujiragi kidnap Shinra, she immediately goes into a rage. This causes her to become a large, black mass that directly correlates to her mental state. It is explained that in this form, unless reunited with her head, Celty will remain a mindless creature. However, when her head is returned, Celty loses all her memories as the Headless Rider and tries to return to her former dullahan duties. Luckily, Shinra sees through Celty's lie as she was only faking memory loss to make leaving easier. He manages in the end to sever her head and Celty returns to normal.
• ERASED is about an adult named Satoru, who Mental Time Travels eighteen years and tries to save his classmate, Kayo, from being murdered. A Running Gag is him getting freaked out because, in his child body, he has a crush on her.
  Satoru: (thinking) DUDE, YOU'RE 29.
• Fullmetal Alchemist: The Conqueror of Shamballa: Implied to be the case with Envy. Originally, while extremely ruthless, Envy enjoyed taunting people, was a Combat Pragmatist, and far more competent than his manga counterpart. In the movie, Envy has been trapped as dragon for the past two years and while he does speak, he mainly roars and hisses. During his battle with Ed, his behaviour more resembles a deranged animal than the arrogant trash-talker he was.
• Himenospia: The queen-ranked wasp mutants can brainwash the females they transform on some level to gain their Undying Loyalty. Niho Kurono is the result of the mortally injured policeman Jirou Kuroda having his brain transplanted into the corpse of a already mutated schoolgirl in order to pretend being converted by Himeno and sabotaging her from within Himenospia. However, the cellular memory of his new female body leaves him unable to directly kill Himeno when he has the chance. Himeno even argues that he's become a whole different person than either his former self or the host he killed.
• Negima! Magister Negi Magi:
  • Evangeline says that she acts much younger than her age because she's been stuck in a ten-year-old body for hundreds of years, and her personality is affected by that form.
  • When Sayo (the ghost of a 15-year-old girl) starts possessing a small doll, she starts acting much more light-hearted and childishly than before.
  • Averted when no one who uses the age-disguising pills ever acts differently unless it's a deliberate act to appear their "age". Ironically, it just makes Negi appear as old as he acts!
  • In a different kind of example, Albireo Imma's Shapeshifter Weapon allows him to become the person he transforms into: all the memories, actions, personality traits and instincts he observes of them are recorded into his many books (he has one for every person he's met). While he's subconsciously aware of his own presence, his body acts completely as the person would, so much that the person themself is essentially speaking. He's able to take over when he needs to, but for the most part the consciousness he imitates is in the driver's seat.
  • Also is Shiori's persona stealing ability which allows her to do largely the same thing, only for her she almost completely blanks out of consciousness to the point of thinking she's the person. However, she does leap instantly to Negi's defense and gets badly injured, though the only one to notice the lack of magic canceling was the Governor General. Also appears to have a crush on Negi... make of that what you will. Shiori is apparently aware, behind the scenes, of what "Asuna" does. But not the other way around, until she starts having feelings for Negi.
• It's more subtle than most examples, but in Parasyte, after Migi infuses himself into Shinichi's heart and bloodstream to save his life, his emotions get duller and duller; he eventually reacts to a dead dog by throwing it in the garbage, earning a What the Hell, Hero? from Murano and making him realize what's happened. This prompts him to get better.
• In Ranma ½, the vast majority of the shapeshifting characters gradually (though not consciously) acclimate to their cursed forms, learning how best to take advantage of their traits (such as size, flight, dexterity, or appearance) and paying heed to their natural instincts.
  • The most notorious example is with Ranma him/herself: although his personality and sexuality remain untouched, he grows considerably more comfortable with his female self, adopting feminine mannerisms and body language. Halfway through the series, (s)he thinks nothing of dressing up nice and going on dates with men (usually for some ulterior motive, but sometimes solely for the guy's benefit) even though the mere thought of wearing a skirt was anathema to him at the beginning of the story. But is it the body working on the mind, or just gradual desensitizing?
    
    In a Filler episode, Ranma gets knocked on the head while in girl form, making "her" believe she's really a girl (an extremely Girly Girl) who unfortunately changes into a boy. This painfully stereotypical behavior is probably just a reflection of Ranma's own mental image of what "normal girls" are supposed to be like.
  • An extreme example is Miss Hinako Ninomiya: due to an unspecified illness when she was a little girl and Happosai's chi-tampering, her body was stuck with the appearance of a ten year-old, even though she's somewhere in her late twenties. She acts like an obnoxious, bratty, bossy, hyperactive child while in kid form, but when she absorbs enough Battle Aura to temporarily restore her adult body, she's much more aloof and calculating.
  • Another good example is Ranma's father Genma, who actually seems to enjoy being a panda more than being a human, even going so far as to eat bamboo shoots.
  • Then there's Rouge, who turns into an Asura — a three-headed, six-armed, fire-breathing demon-goddess. Normally, she's a kind-hearted Chinese Girl, but in her cursed form she's got a case of A God Am I, and her temper disappears. Her irritability is partially explained as a result of the agonizing back-aches caused by having three sets of shoulders. In contrast, Pantyhose Taro turns from bishonen to minotaur-freakshow, without the slightest change in his Jerkass personality, although he seems less calculating and more instinctive as a chimera. In his case, he was baptised in the cursed spring soon after he was born. Changing from human to minotaur and back again for all your life is bound to result in a more consistent personality.
  • Kinnii, the killer from Jusenkyo, is probably hit by this trope as much as, if not more than, Rouge. A weapon of mass destruction for the "Jusenkyo Preservation Society", he's bulking, bloodthirsty and skilled with his sword; when he shapeshifts into a highly moral priest, he's nothing but a timid and regretful Nature Lover, who couldn't even believe (or likely remember) what his natural form is capable of.
• In Show by Rock!!, Cyan is a human who was turned into a Cat Girl. She finds herself involuntarily performing cat mannerisms like meowing at times.
• Used and subverted in The World God Only Knows. After a gender bending "Freaky Friday" Flip, the boy begins acting more feminine and gains an interest in dating sims for women. However, this is because the evil spirit inhabiting the girl's body is manipulating his emotions as the girl has no such problems while in his body. May also be the case for the goddesses unless Keima really is that much of a chick magnet. Diana has turned tsundere for Keima and Vulcan appears to be following suit.
• Inugami Hatsune, a member of Psychic Squad Esper team "The Hound," suffers from this. Her powers allow her to technically assume the form of an animal (typically a canine) but the longer she spends in a form the more animal-like she becomes. Generally, the only way to snap her out of it is to calm her down by feeding her. This is the task of her partner, Yadorigi Akira, whose mind-switch powers allow him to throw prey in front of her to catch (and also forces him to experience the feeling of prey being eaten each time).
• Once you become a vampire in the world of Kurobara Alice, you retain your old memories — but your mindset starts changing. In Dimitri's case, he becomes less emotional and more regal as the "heir" of the deceased vampire leader, Lord Bradley; when the story sets in the present, he's pretty much an Emotionless Boy.
• In Fairy Tail: 100 Years Quest, most of the main characters, save Natsu and Gray, get transformed into youkai after being captured by the villain's minions. The process completely inverts their existing personalities, as they all turn violent and sadistic, happily self-identifying as their new forms, and seeming willing to remain youkai permanently. After they get turned back, they also don't retain any of those memories.

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