Anya Emerson was first seen in "The Wish", as Anyanka a vengence demon. Giles detoryed her power centre her amulet and her superiors  such as D'Hoffyn refusing to change her back as Anya is stuck in Sunnydale as a mortal. She lies to Willow about her necklace telling her its a family heirloom and asks her to help get it back with a spell.
But instead evil vamp Willow appears. Anya is now stuck in this world without her powers so she starts to make some adjustments such as inviting Xander to the prom.
In season 4, Anya and Xander start to have a relationship. In continues throughout the season and into season 5. In the season finale of season 5, Xander asks Anya will she marry him. She says yes, then no and yes and no and then she says give the ring to me after the world doesn't end. Xander and Anya's Wedding day approached but Xander left her at the altar leaving her heartbroken and crying to D'hoffyn.
Anya learns to deal with the pain and becoms a demon again, her and Xander learn to get a long and cope.
Anya tries to cast a spell on Xander for for what he did but it doesn't work, she can't do vengence on Xander only someone else can. Anya ends up having sex with Spike and Xander finds out and so does everyone else.
When Willow turns evil Anya helps Buffy and the rest of the gang help Willow only because she is worried about her. After Willow is held by magic and can't move Willow makes Anya undo the binding spell.
When the world is saved by Xander, Anya is suprised , she never thought he could save the world.
In the following year Anya continues doing vengence until she decides to undo a spell she casts and in return she will die except D'hoffyn kills her best friend Halfrek instead.
Anya stayed true to the Scoobies from then on and played her part, added humour to the situations as like Andrew and Xander did. Xander and Anya drew closer together but never too close, they knew they both loved each other dearly but things were different now. They did sleep together again and remain very good friends too.
Anya still fought the good fight right till the end, the very final battle but she went out with the final battle and a bringer stole her life.
No one will forget her, they will remember what a great, funny girl she was.

Andrew: She was incredible. She died saving my life.
Xander: That's my girl. Always doing the stupid thing.

(Andrew may have made up and told many lies and stories in his life on the show but the story he told Xander about Anya was a way of showing not all Andrew's stories were bad and harmed people.)

Rest in peace sweet Anya.
Date of Birth: Unknown
Place of Birth: Unknown
Occupation: Fights evil