Eriko Miura visits her older sister Chisato Shoda's house. The two sisters reunite after a long time, enjoying lively conversation with their families. But by chance, Eriko's son, Tatsuya, catches Chisato in the act of masturbating. Shocked by the incident, Chisato can no longer suppress her hidden desires and gives in to her urges, seducing her nephew. As their forbidden passion spirals out of control, the boundaries between family and lover blur, escalating into an intense, taboo-laden incestuous relationship that entangles both mother and daughter in a web of desire.