Shin Karino is an unpopular manga writer and he is single. He lives in an apartment complex that has a rule forbidding children from living there. One day, Shin Karino's doorbell rings. When he opens his apartment door, he sees a small boy. The boy is 5-year-old Kotaro Sato. Kotaro Sato tells Shin Karino that he moved into the neighborhood. Shin Karino makes a weird face, because of the rule of his apartment complex. Kotaro Sato says that he lives by himself. At first, Shin Karino is annoyed by Kotaro Sato, but residents of the apartment building, including Shin Karino, become attached to Kotaro Sato.