Saya Otonashi is a seemingly ordinary 16yr old girl with amnesia who has been living with a foster family for the last year. One day she is attacked by a monster and finds out her blood is the only thing that can kill them. Saya embarks on a journey with her family, allies, and Chevalier Haji to remember her past and to rid the world of the Chiropteran threat even if it means risking everything.