The main character, university student Yasutaka Eda, had painful memory. When he goes to the room of Yumi Shibasawa, with who he has been dating, he finds her in the embrace of another man he has never seen before. However, Yumi did not hide it and continued to have sex with a man in front of him, telling him that the reason for this was because she was not satisfied with what he was doing with her. The relationship ended and Yumi disappeared from the university, but the shock remained. He was convinced that he would never be able to make a girlfriend again. Later, he reunites with Yumi’s sister, Mia Shibasawa. They gradually became attracted to each other and started dating, but the trauma Yumi had inflicted on Yasutaka remained and affected their sex life. However, Mia has been there for Yasutaka, and his wounds have finally healed.
A short time later, Yumi reappears in front of Yasutaka. Yasutaka told her that his current girlfriend is his sister Mia, and Yumi had no problem with that. I thought I could forget about the past and continue to live happily with Mia. However, Saginuma Soma, the man who had sex with Yumi in front of him in the past, gets not only Yumi but also Mia, who was supposed to love only Yasutaka, involved in the world of sexual desire.