Dawn Summers
Dawn Summers was introduced as Buffy's sister in season five. A magical energy source known as the "Key" was transformed by the monks that protected it and sent to Buffy in human form. The key was created to tear down the boundries between dimensions and the hellgod Glory would use it to get home.
In human form Dawn is pretty much a typical teenager: short tempered with a "no one understands me" attitude. She spends most of her time in some sort of trouble that Buffy needs to save her from.
Stats:
Classification: Currently Human
Powers: Originally the destroyer of the universe, currently none.
Not yet a full fledged member of the Scooby Gang, though she would like to be.
Job: Still in highschool
Love Interests: Xander, Spike