Shiori, a married woman living with her husband and daughter, finds herself dissatisfied with their sexless life. One day, she accidentally catches a glimpse of her son-in-law masturbating, revealing an enormous penis that captivates her heart. Unable to resist its allure, she becomes obsessed with teasing him at every opportunity, even when he's tired from being neglected by his wife. Eventually, her son-in-law can no longer contain himself and gives in to his desires, seeking comfort in her naughty advances. As they continue their illicit relationship behind closed doors, both find solace in each other's company, leading them down a path of forbidden pleasure.