Kou Yamori seems like a typical middle school student on the surface. Relatively good at studies and amiable with his classmates, he puts a lot of effort into maintaining this facade. One day, however, he decides to stop pretending and quits school, developing insomnia as a result of having no daytime outlet for his energy. When taking walks alone at night, he feels marginally better, though he is aware that his inability to sleep should be considered a serious problem.
On one such walk, Kou meets a weird girl, Nazuna Nanakusa, who diagnoses the cause of his sleeplessness: despite making changes in his life, he is still holding himself back from experiencing true freedom. She says that he won't be able to sleep unless he is satisfied with how he spends his waking hours. When it appears that she has resolved his current worries, Nazuna invites him back to her apartment to share her futon. After a while, unaware that he is only feigning unconsciousness, she leans over him—and bites his neck!