Riho is a high school student who has come to Tokyo to take an entrance exam there. During her stay, she is taken in by the Kimura family, who are relatives of Riho. The Kimura family has a son named Ichiro who is a dull student who is retaking entrance exams. He doesn't study every day, he just masturbates and there is no sign of his academic performance improving. Riho and Ichiro are reunited for the first time in about 10 years, but in the time they haven't seen each other, their cousin has grown into a spectacular pair of breasts. Ichiro remembers how they used to take baths and sleep together, and he casts passionate glances at Riho's breasts.