The two couples, Asuka and Kousuke as well as Kanade and Reiji, have been friends for a long time but haven’t had a double date since they were still unmarried students back then. They want to change that now, so they have decided to visit an onsen together. While enjoying dinner together and talking about their sex lives, the four realise there are some differences and conflicts. So, in the end, they want to try swapping partners for at least one night to bring some variety into things. During this long night, however, they have to realise that they might even like each other’s partners better than their own …