Anya / Anyanka

When Cordelia catches Xander cheating, her pain brings Anyanka, a vengeance demon, to town. She poses as a student and Cordelia wishes thatBuffy had never came to Sunnydale. Anyanka shows she is more than what she seems and creates an alternate universe. Giles stops her by destroying her powercenter, which breaks the spell and makes her human.
Now stuck in a mortal body, Anya hangs around in Sunndyale, trying to get her powers back. She ironically starts dating Xander who helps her adjust to her newfound humanity.
Anya is in fact very strange. Although she herself was responsible for many atrocities, she is petrified of bunnies. She is very blunt and straightforward, and obsessed by money. She works at the Magic Box with Giles and plans to marry Xander, but when he disappears on the day of their wedding, Anya becomes a vengeance demon once more, although she is not nearly as evil as she once was. She shows her love for humankind by sacrificing herself to save Andrew in Chosen.