Shinji Kanou is your average university student: dull, lazy, and excellent at procrastination. He spends the days mingling with his few friends and the nights with his porn collection, yearning for a female companion. His days of solitude come to an end when the beautiful and busty Yumi Mishima and her family move into the apartment above him.

After an awkward and erotic meeting, a series of fortunate mishaps follow, and Shinji finds himself as Yumi's sex friend. Joined by Yumi's identical twin, Nami Ootake, the raunchy trio indulges in sexual activities daily behind the backs of their friends and family.