Amu, a high school student who came to Tokyo for her exams, is staying with her relatives, the Kawasaki family. The family includes Satoru, a ronin son who spends most of his days not studying, but masturbating in front of his computer. When Amu and Satoru reunite after years apart, he can't help but notice how incredibly large Amu's breasts have become. Remembering their close childhood bond—how they used to bathe and sleep together—Satoru becomes overwhelmingly curious and desperate to see his cousin's huge tits.