Arisa lives with her husband, daughter, and son-in-law Haruhiro. One day, Haruhiro confides in her about his dissatisfaction with their daughter. Wanting happiness for the couple, Arisa agrees to help him investigate their daughter's private life. But as they spend more time together, Haruhiro becomes captivated by Arisa's voluptuous figure, gradually forgetting their original purpose. His feelings shift from concern to desire, and he becomes obsessed with Arisa's massive, explosive breasts...