link, the core antagonist of Fruits Basket. I really used to hate him/her, but by the time she resolved her issues in the manga and became the person she really should have been all along, I began to forgive her. But s/he left so many scars behind in his/her path, both anime and manga. Rin did not as readily forgive her as the other Zodiac members did, but with a good excuse: Akito pushed her out a window just to force her out of her relationship with Haru. However, she really proved herself to me when she went to get help after Tohru fell off the cliff in book 21. At that point I realized she had changed and was not going to take out all the pent-up anger she had due to her mother on the other Zodiac members. Although in the end Akito reconciled and became good, s/he still counts as an antagonist and is therefore my favorite.
Note: In case any Fruits Basket fans out there who have not read the manga and are curious/confused as to why I was referring to Akito as female, it's because, well... Just read the manga. It's easier.