Sisters Ryouko and Jino reunite at their childhood home for their late father's memorial service. Ryouko, still haunted by her past affair with her brother-in-law, gives in to temptation and seduces Jino's husband upon his arrival. Meanwhile, Jino is caught masturbating in the kitchen by Ryouko's husband and is forcibly taken by him. During the chaos, their sons each witness secret trysts—Ryouko with their own father, and Jino with her uncle—and as the family's moral boundaries collapse, the boys take action in a desperate attempt to stop the spiral of incestuous desire.