Yuna & Masashi and Ai & Terudai are couples who attend the same university and are in the same club. They often go on couple dates and are good friends. As their anniversaries are coming up, the four of them come on a trip. Even though they know it's wrong, Yuna and Terudai secretly have sex on a two-day, one-night trip without telling their boyfriend or girlfriend. "I love my boyfriend, but my sexual chemistry with my best friend's boyfriend was the best..."