Kite Liberator

In the previous series "Kite", a killer — Sawa — suddenly disappears after she avenges her parents' death, and no one knows where she is. Several years later, a figure dances airily on the dark side of a big city. She is an angel of death, killing her victim gracefully and disappearing. Monaka is a normal high school student, though this quiet and modest life has a darker side. An angel of death is Monaka's other persona. Source MyAnimeList