The Hatano couple, who have just moved into the floor below, come to greet the Otsuki couple who live upstairs. The moment the Otsuki couple see the two, their desires awaken. After making sure that Yui is not there, Hibiki barges into Yui's house and succeeds in seducing Yui husband. Hibiki enjoys sex with both her husband and Yui's husband, and one day she invites the Hatano couple to dinner at the Otsuki house and reveals her relationship with Yui's husband. When Yui finds out, she ends up having sex with the Otsuki couple. What will become of the relationship between the two couples?