Amnesiac high schooler Saya Otonashi has spent years living an ordinary, uneventful life on Okinawa with her adoptive family, including her brother Kai Miyagusuku, until a Chiropteran, a blood-feeding, bat-like creature, attacks her school. Hagi, a silent stranger who has apparently been searching for her, arrives with a sword and the claim that only her blood can destroy the creatures. This manga adapts the same story as the 2005 TV anime.