As the Underwear Society make preparations for the drama club, they are asked to participate in the performance. After school, Nayu runs into Kiyono, who had heard about Keigo's job offer. The next day, Nayu takes on some extra work whilst Kiyono tells Hiroki about Nayu's apparent transfer. He confronts Nayu about this, who asks him to stay quiet until after the festival. On the day of the festival, Tsukamoto confronts Mizuno and Nayu about the society's appearance in the magazine. She asks the play to be cancelled, but Mizuno stands up to her and tells her to hold her judgement until after she's seen their work. However, during her inspection, Nayu's old elementary school teacher comes in a berates Nayu. Thankfully, both the society members and Tsukamoto stand up to him, the latter of which allows the play to take place. After a successful performance, Nayu tells Yako and Haruka that she's transferring as Keigo tells Mizuno the same thing.
The story revolves around Nayu Hayama, who embarrasses herself on the first day of middle school by accidentally showing her adult panties. As two other students, Yako Jingūji and Haruka Shiraishi, hear rumors of her engaging in "enjo kōsai", or compensated dating (which often is viewed as being close to or the same as prostitution), they investigate. They soon learn that Nayu is an 'underwear monitor' who tests new underwear products, and has great insight on what underwear people should wear. Nayu hopes to help everyone get through the vital stage of their life by opening an underwear club.
