Rina tells the nerdy Nanashi boy to abstain from masturbation until the next assembly. One day, when he’s holding back to the limit, Rina says, “Let me do it right now,” and Nanashi’s heart skips a beat. A foursome with Rina, Megu, and Mio in their gym clothes begins, and Nanashi’s excitement reaches a fever pitch! But then the busty teacher Yuuka arrives, and the four of them hurriedly hide in the lockers…? Peeking at the girls changing from the locker room, he finds himself in a packed train with the girls in their gym clothes! Nanashi’s reason is on the verge of exploding…!