Hibiki is a young married woman living a calm and happy married life. One day, she sees her husband's college friend staying over, and notices he's already erect in the morning. Shocked by the sight, she's both surprised and aroused by the huge cock she's never seen before. Her mind gradually begins to waver, and as she's pounded intensely, she's shown climaxing repeatedly. As her body becomes accustomed to sex with the big dick, she's increasingly drawn into its irresistible allure.