Sisters Ryoko and Izumi gather at their parents' house with their entire families for the memorial service of their late father. Ryoko cannot forget the sweet memories of her past relationship with her brother-in-law, and ends up seducing Izumi's husband when they meet again. Meanwhile, Izumi, the younger sister, is caught masturbating secretly in the kitchen by Ryoko's husband, and ends up being raped. The sons, who witnessed their aunt and their own father engaging in sexual acts, step up to prevent the collapse of their family...