Anya was, about 1120 years ago, a girl � a girl who'd been dumped and was practicing vengeance spells on men (boils on the penis and other fun stuff). The demon D'Hoffryn got wind of her, and made her a vengeance demon. She carried out her duties for over a thousand years, known as Anyanka, the patron saint of scorned women. She found women who'd been hurt by a man, used a special necklace (her power center) to grant their wishes. Usually, the wishes involved vengeance on the man who'd betrayed them. Anyanka came to Sunnydale to grant a wish for Cordelia after Xander had cheated on her with Willow, but instead of wishing something bad on Xander, Cordelia wished that Buffy Summers had never come to Sunnydale. Anyanka granted the wish, resulting in an alternate reality. Unfortunately for Anyanka, Giles smashed her necklace, bringing Sunnydale back to its normal reality, and leaving Anya stuck in the mortal body of a teenager. D'Hoffryn refused to give her her powers back, and her attempt to use Willow to help her get her necklace back backfired, so Anya continued attending Sunnydale High School. She developed a crush on Xander, and the two are now a (very sexually active) couple. Eventually, much to her delight, Xander proposed to her and she accepted. Giles also hired her to work at his shop, the Magic Box, a job which she is very good at. She's still working on behaving with humanity, which Xander tries to help her with.