Mizuki and her boyfriend Kazuya, who are about to get married, are a happy couple, but Mizuki has a strong libido, and her boyfriend's sex is not enough and she was masturbating in secret. Kazuya, who has dreamed of studying abroad, invites Michael, a black man who has taken care of him, to his house, and the life of the three of them begins. Mizuki accidentally sees Michael's big dick and is so curious about it that she crosses the line.