Fruits Basket, all the way.
I never really got into manga or anime, even with all the kids I knew who loved Sailor Moon and others. A couple years ago, a friend/coworker invited me to watch Fruits Basket at her house. I got so hooked, I asked to borrow the rest of it and finished watching them by myself. I found the anime very helpful in understanding the storyline before reading the manga. I haven't finished the last ~6 books, so please don't write any spoilers here.
My favorite (and one I identify most with) is Kyo. I think he's the most aspie-ish, if any of them could be put on the spectrum. I can't help feeling a little bit connected to the tiger, Kisa, too....the way Tohru realizes and explains to Kisa's mom exactly how Kisa feels was dead-on. And Momiji, the blond boy who turns into a rabbit! Poor kid. I was in tears when he finished telling Tohru his story. However, I think I would most enjoy dressing up as the boy who turns into a cow, if I ever went to the local anime convention.
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"What's comin' will come, an' we'll meet it when it does." --Rubeus Hagrid (Harry Potter)