Mary and Masaharu are step mother and son. Mary is beautiful, and being close in age, Masaharu has developed intense romantic feelings for her. However, she exudes strong maternal warmth, and though overwhelmed by her allure, Masaharu has struggled to suppress his sexual desire. Yet this uncontrollable emotion gradually consumes his mind and body, until he can no longer endure it. Ultimately, Masaharu decides to leave home, and as a final farewell, the three family members embark on a hot spring trip together. This journey was meant to be his last attempt to sever his forbidden feelings—but the outcome exceeds all expectations.