A human may become a vampire only if they fall in love with one—and 14-year-old Kou Yamori wishes for nothing more. Kou has decided to fall in love with a vampire named Nazuna Nanakusa, and he has only 10 months of nightly rendezvous left to realize his goal.

Kou's friends, Mahiru Seki and Akira Asai, are slowly coming to terms with the existence of vampires and Kou's decision to become one. As Kou realizes that a woman close to Mahiru is a vampire, he is unsure whether to support this relationship.

Meanwhile, Anko Uguisu, the human detective bent on killing vampires, closes in on Nazuna and her coven. When an encounter leaves one of the vampires seriously injured, they learn that their human memories hold the key to a weakness that can be their demise—and to protect Nazuna, Kou must find out about her past.