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.
— Description from AniList community (anilist.co).
