Mizuki and her boyfriend Kazuya are a happy couple who are about to get married, but Mizuki has a strong sexual desire and is not satisfied with the sex her boyfriend has, so she masturbates in secret. Kazuya, who had dreamed of studying abroad, invites Michael, a black man who took care of her, to her house, and the three of them begin to live together. After Mizuki accidentally sees Michael's big dick, she becomes obsessed with it and goes overboard.