Takuya, a college student, finds himself unexpectedly attracted to his older stepsister, Aika, a former delinquent and nursing mother who has returned to the family home. Aika's provocative behavior and lack of boundaries lead the two into a risky, clandestine sexual affair. Despite her guilt toward her husband and children, Aika becomes addicted to Takuya's advances, leading to a dangerous game of secrecy and forbidden passion within their own household.