As she approaches her graduation next year, her boyfriend Yuta has even kissed her, but nothing beyond that has happened yet. He had promised that they would have a physical relationship only when they were adults. When Rimu comes to her boyfriend's house to play, she meets Yuuta's father, Toru, who treats her as kindly as if he were her daughter. That day, the train stops and Rimu is unable to return home, so she suddenly has to stay overnight. The next day, while his girlfriend Yuuta is away, Tooru gives Rimu an aphrodisiac.