He is seduced by his girlfriend's Ke'ai friend, who he should never touch, and has an affair with her! His girlfriend, Masami, who he lives with, is going on a trip for about a week, so Makoto is going to be alone for the first time in a long time. However, her friend Yuuki comes to a drinking party she holds before she leaves, and while she is drunk and asleep, he and Makoto suddenly become close. After she goes on a trip, Yuuki comes to visit again, and for the week until she comes back, they start living together and having sex every day...