The Kajiura couple, Kouki and Risa were trying their best to have a child. However, it didn't go well because Kouki wasn't able to get an erection and Risa's body wasn't responding to her husband. In the end, they returned to their usual day-to-day life. But they didn't want to let it stay like this anymore, so they tried to learn more about a marriage couple sexual intercourse​. That was when they found out about the "sex seminar". Kouki tried to convince his wife to attend this sex seminar. His wife was negative about it at first, but became convinced after listening to the explanation from the instructor. At the seminar, they eventually met the Sonoda couple, Yousuke and Shiho, and participated in a group session. Both couples discussed their sexual troubles and got along really well, even kept in touch with each other outside the seminar. And then one day, as part of the course, the participants had to exchange their partners with each other. Thus begins the path of willingly swapping​... [Translated and edited from the Official website]