Amu is a high school student who has come to Tokyo to take an entrance exam there. She is taken in by the Kawasaki family, who are Amu's relatives. The Kawasaki family has a son named Shintaro who is a repeat student, but instead of studying every day he spends his days masturbating in front of his computer, leading an unproductive life. Meanwhile, Amu and Shintaro are reunited after a long time, but Shintaro notices that his cousin's breasts are in a terrible state. Shintaro remembers that they used to often take baths and sleep together, and he can't help but want to see Amu's breasts.