His girlfriend's best friend, who he shouldn't touch, is too erotic, so he gives in to temptation and ends up having sex with her! His girlfriend, who he lives with, is going on a family trip for a week, so he's going to be alone for the first time in a while. However, her friend Sumire, who came to a drinking party she hosted before she left, and while she was drunk and sleeping, they suddenly became close. Then, when she left on her trip, Sumire contacted him and said she was coming over, so they began a daily cohabitation life until she returned, where they had sex every day...