Ten years have passed since their mother passed away. Her husband was Mizuno Hideo. The two began living together as a family of three, with him as their stepfather. Hideo was kind at first, but his attachment to them grew stronger with each passing day, and now his grip on them has gone beyond restraint to something that could be described as dominance. The elder sister, Natsuko, is 35, and the younger, Kozue, is 30. Having given up on a normal life, the only pleasure they have is to have sex together as sisters. Is it dependence or compensation? What awaits them at the end of this endless pleasure?