Jotaro Kujo (JJBA). Specifically this headcanon started because we both share a common love of slash special interest in dolphins and the sea, which is a huge reason why he’s my favorite, but not the only reason I think he’s autistic. If anything, it was just the nail in the diagnosis. Not that I think he WOULD get a diagnosis, what with him being a teen in the 80s.
Star Platinum’s skill, along with punching and yelling, is noticing tiny details that other people don’t. One of the first things he (through Star Platinum) did was notice a bug in the background of a dark photo and then draw it so perfectly accurate that it could be correctly identified. Yes he was using literal superpowers but Star Platinum IS Jotaro Kujo. You can’t separate the autism from his fighting spirit.
He’s also got a few stims. I’m more of an “Oh jeez
” guy myself but I swear I use it just as much and in exactly the same context as my guy uses “Yare yare daze”. “ORA ORA ORA” is absolutely a stim. In the second OP of Stardust Crusaders there’s a part where the whole cast copies Jotaro’s battle cry the same way me and my autistic friends or family members copy each others’ vocal stims. Which honestly is very sweet and I love it even if it kind of makes me cringe too.
Jotaro has the facade of a cool, tough guy, something that he’s definitely played into (especially in his teens) but it’s canon that he doesn’t really express his emotions and often gets misunderstood because of it. Anyone can see he clearly loves his family and friends and would do anything for them. And who among us hasn’t been misread as aggressive or threatening or unemotional at some point?
I’d also argue he lashes out at women/girls crowding him because it’s overstimulating for him. In part 3 he only lashes out after his classmates start screaming around him. I’ve definitely panicked when too many people are in my business or yelled at them if they touched me unexpectedly. Yeah, obviously it's not great behavior, but lets be real; sometimes you have to have a bit of a meltdown for NTs to take your problems seriously... or at least acknowledge that there IS a problem, even if they think that problem is you.
Also, being a cartoon character aside, we see him specifically mention buying exact replacements when his clothes are damaged, even if it costs him a lot of money and means wearing all black from head to toe through a literal desert. Maybe it's comforting. I'd certainly spend money to keep wearing my favorite outfits if I could afford it.
Otherwise? Weather Report, Rohan Kishibe, Giorno Giovanna, and FF are all pretty common headcanons I assume. There’s a lot of weirdos in JJBA. And idk if I’ve seen any Father Pucci theories, but I believe he’s one of us too. My source? It’s mostly just vibes. I’ve known multiple autistic Catholics and have heard my old therapist lament my “autistic sense of justice” session after session.
I actually have a really long list on my old phone of all the characters I think are autistic, but I really like talking about Jotaro. Hopefully this post isn't too long.