In a world where a small number of people are demi-humans, biology teacher Tetsuo Takahashi is surprised to find his school's new maths teacher is one such demi-human; a succubus named Sakie Satō. As Tetsuo struggles to talk with Sakie due to the measures she takes to keep her powers under control, one of his new students, a vampire named Hikari Takanashi, asks for his help in carrying the headless body of her dullahan classmate Kyōko Machi to the nurse's office...