Kou Yamori is a middle school student who struggles to understand love and finds little meaning in conforming to society’s expectations. Feeling disconnected, he stops attending school and develops insomnia, leading him to wander the streets alone at night.

During one of his nightly walks, Kou meets a mysterious girl named Nazuna Nanakusa, who believes people stay awake at night because they are dissatisfied with their daily lives. She offers to help Kou with his insomnia and invites him to her place, where she convinces him to share a futon. However, just as Kou pretends to sleep, Nazuna bites his neck, revealing herself to be a vampire.

Kou assumes this bite will turn him into a vampire, but Nazuna explains that transformation is not that simple—it requires him to be bitten by someone he loves. Determined to escape his mundane existence, Kou sets a new goal: to fall in love with Nazuna and become a vampire.