"Amu", a high school student who came to Tokyo to take an examination in Tokyo. The recipient is the "Kawasaki family", a relative of "Amu". The "Kawasaki family" has a son named "Shintaro" who lives a ronin, but he lives an unproductive life because he only masturbates in front of a computer without studying every day. Meanwhile, "Amu" and "Shintaro" reunited for the first time in a long time, but "Shintaro" notices that his cousin's boobs are ridiculous. "Shintaro" remembered that he used to take a bath and sleep together, and he couldn't help but want to see "Amu"'s boobs.