Hana, a high school girl who came to Tokyo for her entrance exams, stays with her relatives, the Nakano family. The household includes their unmotivated ronin son Masaru, who spends his days idling away in front of the PC, masturbating. Reuniting after years apart, Masaru is shocked to discover that his once ordinary cousin has transformed into an unbelievably well-endowed beauty with massive, explosive breasts. Recalling their close childhood bond—bathing and sleeping together—he can't resist touching her breasts, giving in to his lustful urges fueled by their familial connection.