I'd also vote for nonbinary Kaworu, especially since he's an alien soul in a human body. And part of the reason Shinji hits it off so fast with him is that not having to compare himself to either strong masculinity or strong femininity makes Kaworu feel less threatening in that regard than almost anyone else in Shinji's life.
Jame from P.C. Hodgell's Kencyrath series, or rather trans AU because I also like canon cis, gender nonconforming Jame too. Jame's a girl who's constantly misgendered as male by virtually everybody so it's not surprising that a young trans woman would find her a very relatable character. Especially if like me you're not very femme so I was all just like Jame is, "I'm not going to act like your idea of femininity so that you gender me correctly." When someone is attracted to her and it's not because they thought she was a cute boy she's really confused, this never happens! I have a whole AU plan in which both her and her brother are trans and I like it.
Spoiler: Mother 3 spoilers Things I was thinking about last night while trying to sleep, so they're moderately incoherent, but. I definitely plaster gender headcanons over any character that's had their identity forcefully erased to better serve someone else's agenda (Winter Soldier, for instance), so Claus gives me gender thoughts. of course it's ambiguous about what actually happened to him, but whatever potential brainwashing was there could have muddled his identity on a gender level as well, if he's super blank-slate-y. so there's the conflict between 'I'm a pigmask, so I'm a man?' (trying to think back, but there weren't any confirmed women pigmasks that I can remember) and 'I'm King P's toy/pet, like all the women in the throne room, so maybe I'm a woman?' both of which are being drowned out by 'I'm an object and neither, stop thinking about it'. if he had lived, he could have had a chance to actually figure it out, but he'd have to deal with the weight of people still expecting him to be the Claus they remember, both in personality and gender, which starts to get a little depressing, mmh. just to add to the genderweird that Mother 3 already has in canon
Continuing the HunterxHunter train @Avery started, I've seen a lot of trans dude Kurapika headcanons. In fact so many that I assumed that it was canon and I just hadn't gotten to where it was revealed (I'm still watching the show). And apparently in the manga Kurapika isn't referred to with gendered pronouns so there's also a lot of agender Kurapika headcanons out there. I've always had the headcanon that Waver Velvet from Fate/Zero is a trans guy. Partly because there's a canonish joke AU where he's a girl, but living with the elitist Archibald assholes instead of his real family, and I choose to interpret that as "in this universe he's with a shitty family who won't let him explore alternate gender identities." And partly because the dude grew from 5'1" to 6'1" between ages 19 and 29 (although I'm not even sure that's possible with T? let's say supplementary magecraft was involved). Edit: Oh, and this is an old one, but is anyone familiar with the Oz series? Princess Ozma of Oz grows up as a boy (very similar to the Zelda/Sheik dynamic, actually) and eventually is found and magically changed back into a girl. A nonbinary Ozma (or gender-questioning Ozma of any sort) would be awesome.
Spoiler: new voltron ep 3 so i headcanoned pidge as being a trans man right from ep 1 and well... i'm half-right. pidge's afab, yeah, but apparently a cis girl? feels weird... first time i get a strong trans headcanon about a character and it ends up both right and wrong at the same time. anyway, onto ep 4!
Tangent, but this reminds me that my main issue with trans headcanons on Tumblr is that they push gender roles super hard, especially when they get insistent that their headcanons are canon. Like, when I was a tomboyish kid, I LOVED Buttercup from PPG--she was a girl like me, who liked Boy Things and getting her hands dirty! And I feel that the whole "Buttercup is a trans boy" thing takes away from that. Characters who don't conform to societal gender roles are important. EDIT: In fact, you know what? Give me more gender nonconforming trans headcanons. Give me things like transmasc!Bubbles who still loves cute animals and plushies and flowers. THAT would be cool as hell.
Yeah, it pisses me off how common that is. Like the "Steven is a trans girl because he wears a dress in that one episode!" crowd.
i would not be surprised if at some point Steven questions his gender identity because he's a gem and all the other gems are genderless/female presenting, but I genuinely don't know how he'd end up feeling about it. Could go any way.
Trans boy!Steven will always be my personal headcanon there and I want to write a fic about it eventually.
*whispers 'same hat' as I dress my subeta avatar in all manner of flowers, ruffles, and other frippery*
Ok, so there's not much behind this headcanon besides "huh his hips seem kind of wide for a (cis)dude," but what if trans Soldier 76? Spoiler: dem hips His uniform also emphasizes his shoulders in a potentially figure-concealing kind of way. And it would be interesting if the supersoldier program that he and Reaper were part of had something to do with his transition? That would explain how ridiculously deep his voice is, at any rate. and maybe imply trans!Reaper as well ovo
*crashes into the thread* MORVEN YOU AND I NEED TO TALK TRANS KNORTH TWINS AU'S RIGHT FUJCKING NOW. @Morven
Ooo, trans 76 is a great headcanon. I'm kind of ridiculously attached to trans dude Reinhardt myself, because he's about the age for being around during the tumblr heyday and I don't see enough trans dudes in media that are swole old men with big beards. Trans Reinhardt supporting all the other babby trans people he knows. He's been there. Lion Grandpa to the rescue.
Oh my gosh, that is the best headcanon. He picked himself the most badass name ever I'm imagining bby Reinhardt on tumblr, Discoursing away, and it is adorable oh man "Lion Grandpa to the rescue" is giving me the warm fuzzies ouo