Sakai and Kokoro are a couple. One day, Sakai goes to her house to play, and meets Aiyu, a busty mother with a busty figure who is showing off her busty figure, and gets excited. When Sakai uses the bathroom in her house, he witnesses Aiyu masturbating while pretending to be Kokoro and calling out his name. Seeing this, Sakai can't contain his excitement and masturbates his erect penis, but Aiyu cums first, leaving him with indigestion. Sakai can't get this incident out of his head, and he pressures Aiyu into a relationship...