Dawn Summers.

About Dawn Summers

Dawn Summers is a fictional character created by Joss Whedon and introduced by Marti Noxon and David Fury on the television series Buffy the Vampire Slayer, portrayed by the late Michelle Trachtenberg. She made her debut in the premiere episode of the show's fifth season and subsequently appeared in every episode of its remaining three seasons. Within the series, Dawn is the younger sister of main character Buffy Summers, a girl chosen by fate to be a vampire Slayer. Whedon introduced Dawn to the series because he wanted to introduce a character with whom Buffy could have an intensely emotional non-romantic relationship.