Hiro Hiyorimi arrives in Sasanaki to join his older sister Sawawa, who has taken a housekeeping job at a mansion in town. He is killed in a traffic accident his first day there, and the mansion's mistress, a noble of the Monster Realm known only as Hime, brings him back with her own blood as her blood warrior. He has to keep drinking it to stay half-alive, serving alongside the android Flandre, Riza Wildman, a werewolf on her father's side, and the vampire Reiri Kamura.