Mizuki and her boyfriend Kazuya, about to get married, are a happy couple, but Mizuki has a strong sexual desire and secretly masturbates because her boyfriend's sex is unsatisfactory. Kazuya, who always dreamed of studying abroad, invited Michael, a black man who took care of him, to his house and the three of them began living together. After Mizuki happened to see Michael's big cock, she got so nervous about it that she went over the edge.