Kou Yamori is an ordinary middle school student who finds it difficult to understand the complicated nature of love. Since he sees little point in conforming to societal norms, he soon stops attending school. Suffering from insomnia caused by his inactivity, Kou starts wandering the empty streets at night. One night, Kou meets a strange girl named Nazuna Nanakusa, who believes that people stay awake at night because they are unhappy with how they spent their day and cannot rest until they let go of their inhibitions. Nazuna offers to help Kou with his sleep problems and invites him to her home, where she persuades him to share a futon with her. Feeling uneasy, Kou only pretends to fall asleep—which is when Nazuna suddenly bites his neck, revealing herself to be a vampire! Although Kou assumes the bite will turn him into a vampire, the details of the transformation are not that straightforward. To change, he must be bitten by someone he truly loves. Prepared to abandon his bleak mortal existence, Kou sets a new goal: he will fall in love with Nazuna and become a vampire himself.