ANYA
Anya came to Sunnydale in the guise of a new transfer student, and befriended Cordelia after Harmony and the Cordettes were mean to Cordy about her relationship with Xander. Anya however, was actually Anyaka, the patron saint of scorned women. She had been drawn to Sunnydale by Cordelia's feelings of betrayal by Xander, and encouraged her to make a wish which would exact revenge upon Xander. What Cordelia wished for was that Buffy had never come to Sunnydale, and she found herself in an alternate Sunnydale. Anyanka lost her power center when it was destroyed in the alternate Sunnydale. She tried to get the necklace back with Willow's help, but the spell was botched and instead of the necklace it brought forth the Evil Willow from the alternate Sunnydale.
Anya returned to the Sunnydale scene when she told Xander that the only way to stop thinking about him was if they were to have sex. In the afterglow when Xander didn't respond the way she wanted him to, Anya stormed off. She continued to see Xander and the two became a couple. Anya started working with Giles at the Magic Box and has become a solid part of the scooby gang, learning - sometimes painfully - how to be a human being.