Anya Emmerson first was introduced in The Wish where she was a vengeance demon and could grant other's wishes with her stone called the Amulet.. She was about 1100-years-old, and was really upset that Xander cheated on her with Willow. Anya went to Cordelia and told her to make a wish, since she thought Cordelia would make a wish for something to happen to Xander. Instead Cordelia wished that Buffy had never come to Sunnydale. The wish went very bad, since demons and vampires were ruling the streets. Finally Giles found the Amulet and broke it, returning everything the way it had been. 
    Anya and Xander got back together. Anya was now an ex-demon because all her powers had been taken away. She is very helpful to the "scooby gang" and is able to know a lot about how to kill some of the demons. In the end of season 5, Xander proposes to Anya, in which Anya accepts.