Kou Yamori is an ordinary junior high student who finds it hard to understand the intricate idea of affection. Since he feels little reason to follow conventional paths, he soon quits attending classes. Struck by sleeplessness from his idle days, Kou starts wandering the empty streets after dark.
His thoughts drift endlessly, and the city lights seem to mock his emptiness. One evening, Kou meets an eccentric girl called Nazuna Nanakusa who thinks that staying awake at night stems from dissatisfaction with daytime actions and a need to free oneself before rest. Nazuna offers to solve Kou"s insomnia and invites him into her apartment, where she persuades him to share a futon. Unsettled, Kou merely pretends to sleep—at which moment Nazuna bites his neck, exposing herself as a vampire!
She claims that vampires feed on the lingering doubts of those who cannot let go. Kou believes the bite will transform him into a nocturnal creature, but the process is more complex. To become one, he must be bitten by someone he truly loves. Determined to abandon his bleak mortal existence, Kou resolves to love Nazuna and turn into a vampire forever.
