Yosuke is Haruka's boyfriend and the two are living together. Yosuke and Haruka work different overtime hours, so the two have very little time together. Yosuke asked Haruka for permission for the two of them to have sex today because it had been a long time since they had done it. Haruka agreed to let Yosuke have fun when he got home from work. After coming home from work and seeing her lover sleeping, today she wore an extremely seductive pair of panties that made Yosuke unable to control himself anymore. While doing so, he saw the face of the girl below, it was Kanon-chan, his girlfriend's younger sister! It turns out she had an argument with her mother today so she came here to hide. But luckily he didn't stay long, tomorrow morning when Yosuke got home from work he would already be home. And Haruka promised to make it up to him for today. When I got home, I saw a naked woman, wrapped only in a towel, coming out of the bathroom. Thinking that his girlfriend had to go home because of Kanon, Yosuke didn't hesitate anymore. He quickly rushed into her, releasing all the discomfort of the past few days. But while he was having fun, the towel slipped off and the girl he was making love to was Kanon! Because of fear and confusion, he lost control and ejaculated all his semen inside his lover's younger sister...