Not really a headcanon so much as it is mapping a canon thing onto an AU version of a character, but: Spoiler: su spoilers Given the whole anti-tattle measure revealed in Gemcation...selectively mute human!Pearl, anyone? Specifically as a trauma response--a literal inability to speak about the Bad Things That Happened.
I've seen at least one AU in which Equius' behaviour was not down to fetishism but to OCD. I don't have OCD but do have intrusive thoughts, and I know enough about compulsions to see that in him. He doesn't seem to actually enjoy following all the rules of behaviour he feels he must follow and even a pubescent boy would probably be able to shut their fetish off when they were about to get murdered.
On further thought I think I determined a root cause for that hypothetical anxiety. Considering how he breaks things so easily and gets so angry about it, he might be thinking that if he's ordered to do something, it isn't his fault if it goes wrong.
Last one, promise; it could also explain his extremely selective manual dexterity. He might have actual coordination issues, but he has no problem working with delicate electronics, probably because he's confident with those and likes them. With, say, drinking from glasses, he's all "don't mess it up don't mess it up don't mess it up SHIT i messed it up" - I get that a lot.
Railrunner, the lead character and accidental villain of Miranda Leek's Twisted! was diagnosed by a reviewer as having Antisocial Personality Disorder:
Can't remember if I've posted this before, but a fanfic on the topic convinced me that Arnold Rimmer has dyscalculia.
Zero/Mikage Reiya from Force of Will has BPD. Behold. My fantastical proof: Zero has abandonment issues. She's very anxious about the idea of Fiethsing leaving her alone, and not just when she dies. Even when it's just a normal day of Fieth being gone she worries and begins to assume that it's because she did something upset Fiethsing and she is purposefully avoiding her. Zero has an unstable sense of self. The most apparent of this is the fact that she doesn't remember being a vampire and that when she does remember this she seems to go out of her way to be as vampirely as possible. Zero also suffers from imposter syndrome though and regularly doubts herself and her abilities. She's also prone to having certain values which she clings to aggressively that she tries to define herself by. "Monsters must be killed" and "I am a knight", for example. Zero has a temper. She gets frequently annoyed and she has explosive bouts of anger, more than most of the cast. While her fits of rage aren't loud and full of screaming, they do involve people being erased from reality. Zero seems to split. Her opinions on people end up falling into one of two extremes, and in particular she's managed to deperson Gill entirely before killing him. Her two biggest concerns on this front are "monsters need to be killed" and "I must protect everyone". Zero has trouble making decisions and what decisions she does make quick tend to be violent and self destructive snap judgments. Unless she's defending one of her own or rushing into suicidal amounts of danger she tends to have a lot of trouble deciding on things. Give her a chance to get herself killed while protecting a loved one though and she will jump at it even if people tell her to fucking not do that. Zero often seems to be depressed or highly anxious. Her view on the world she lives in is very pessimistic and she's frequently shown worrying that she can't protect it. Life is one of infinite possibility, but to Zero all those possibilities are negative. Zero's father is a controlling murderous vampire who is abusive towards his daughters. She was also the prize jewel of the family in terms of power levels of his children and her environment would've been one of death, violence, and deceit constantly.
Can we also bold "self-destructive and dangerous behaviours", given that at least twice (with Gamzee and with Lord English) he hurled himself directly at the opponent without thinking and immediately got killed, and also his strategy for SGrub was noted to be "fight first, ask questions later"?
I only just realized I never posted this back when Oathbringer came out, but I would not be surprised if Shallan Davar from the Stormlight Archive has BPD complicated by her illusion magic. We already knew she had anxiety, PTSD, and a tendency to dissociate and repress memories (often deliberately), and that all her brainweird issues are bound up in complicated ways with her magic. Spoiler In Oathbringer, though, she starts having severe identity issues; she'd already created a persona of a con woman to be able to do undercover investigation, and she ends up creating a second persona to insulate herself from a severe trigger she can't avoid. She just dissociates and subsumes herself into being Brightness Radiant, who is a proper knight who only cares about battle, because Brightness Radiant wouldn't flip out over learning to use a sword the way Shallan would. And then any feeling or desire she can't express as Shallan the scholar/artist or Brightness Radiant gets sunk into being Veil the con woman, and she starts losing control of which one she is at any given time. Since Shallan's magic and mindset are also bound up with her art, this even extends to drawing horrible stick figures when she's sketching on several occasions because she was being Veil mentally and Veil isn't an artist. She actually catches herself at one point trying to make a character to act who's good at studying and has to remind herself that Shallan is a scholar who's good at studying. Her sense of who she is is obviously really shaky and getting shakier, and she does a fair bit of reckless acting out over the course of the book to try to shore it up. Notably, when her mentor who everyone thought was dead and who (acts like she) has never experienced a moment of doubt or low self-esteem in her entire life turns up and goes right back to treating Shallan like her student, the feeling of invalidation gets to Shallan so badly that she immediately decides to volunteer for a super-dangerous undercover mission just to not be where her mentor is/prove that she can do stuff on her own. Basically I need to find, like, anyone who has read both Stormlight and Umineko so someone can appreciate my Shallanatrice jokes.
Arnold Rimmer has canonically had what appear to be dissociation and panic attacks, as demonstrated in this fic expanding on a canonical incident.
I don't know if Vriska might be an actual sociopath or psychopath. She seems to fit the criteria to me, but I don't know enough about those conditions or her to tell for sure. I don't know how much of it is her putting up a front, and I also don't know how much of it is Hussie dropping the ball with writing at the end because my resentment of the ending is colouring my view. I could also see her as having Reactive Attachment Disorder; (Vriska) seems to be sort of overcoming it at least a little. (Vriska) got upset without getting angry, so that may be a sign she's not in the sociopath/psychopath bracket?
Okay, so: Majima has PTSD, this is canon and clearly represnted in the games, all of them do to one degree or another because A LIFE OF CRIME IS DEEPLY VIOLENT AND UNFORGIVING but: Bipolar I, rapid cycling. Most of the time he only swings up to hypomanic, but full-blown mania doesn't seem out of the question; a lot of this is trauma-influenced, and he's gotten good at mmmostly hiding his downswings versus his upswings, but he still definitely has them and they absolutely influence his behavior. His wildest, most outrageous behavior is during a manic episode, with the same kind of hyperfocus on a Specific Thing that sometimes comes with mania--in Yakuza Kiwami, that's the Majima Everywhere mechanic, where the focus of all that energy and attention is Kiryu, god help him.
I feel like there's probably some ground to explore re: bipolar Victor Frankenstein and the most over-the-top manic episode in history.
(Like, we all know the "obsessed mad scientist" trope that more or less originates in Frankenstein, but in the original novel, as soon as he actually makes the monster, he immediately spirals off into a complete physical and emotional breakdown that results in him having to be nursed back to health by his conveniently-arrived best friend, because ever since he suddenly became convinced that he knew the secrets of the universe he hasn't been eating, sleeping, going outside, or talking to people. He describes himself as emaciated, feverish, and jumping at falling leaves, and finds the entire idea of science so upsetting afterward that he switches to studying Turkish poetry with his friend instead.)
not trusting myself with slapping wholeass diagnoses onto characters but Rodimus Transformers has some sort of space executive dysfunction and over the millenia has invented increasingly more dramatic ways of making that phase of "i want to, but my brain is dead" clear as crystal.
