Mutsuki, who works at a hotel front desk, is very close to her younger brother Rintaro. So close that they are comfortable being naked in front of each other. Rintaro is still a high school student who lives with his girlfriend. Shigeya Yoshida, an affluent architectural designer in Yokohama, likes Mutsuki and begins an affair with her. His wife, Hideyo, finds out about them and is very jealous, and seduces Rintaro to have her revenge. In addition, Hideyo has a younger brother named Kiyoshi who has feelings similar to love for his sister. All of these intertwining affairs and emotions will lead to a climactic ending among all the persons involved.
20:45, 29:56 - Mutsuki begins an affair and fucks a hotel guest, the affluent Shigeya.
45:36 - Mutsuki finally acknowledges her younger brother Rintaro's feelings for her and they start to have incestual sex, but it doesn't finish.
51:08 - Hideyo, Shigeya's wife, discovers his affair with Mutsuki and goes to Rintaro's house to seduce him as part of her revenge.
53:07 - Mutsuki and Shigeya fuck in the bathtub at his mansion. In the next scene, Hideyo brings Rintaro to the mansion too and they start fucking while Mutsuhi and Shigeya are hanging out in the front yard. Suddenly, Mutsuhi and Shigeya see two men fighting on the balcony of the house. They run inside and find Rintaro unconscious on the floor, and Hideyo and her own brother Kiyoshi, who always had an incestual desire for her, fucking on the couch!