A Japanese high school class is forced by their foreign teacher to attend a school trip to Europe. But the trip is not what they expected when their teacher, Suomi, decides to take them all to the nudist beach where she grew up. Since they all must be completely naked—and to avoid any disrespectful behavior—Suomi imposes one simple rule for the male students to follow: it is forbidden for any of them to have erections. In an attempt to enforce the rule, Suomi pairs female students with the boys so that those with erections can relieve themselves. To everyone's surprise, class president Naotatsu Nagato is the first and only person to break the one rule they were supposed to follow. While his female classmates try to calm his big, kinky, and continual erections, love confessions and answers that Naotatsu is desperately seeking begin to reveal themselves.