Anon, a closeted introvert with a secret panty fetish, finds his quiet life turned upside down when three popular classmates—Rina, Megu, and Mio—crash his apartment. After discovering his collection of adult magazines, the girls decide to put his knowledge to the test, leading to an unexpected and erotic encounter that transforms their relationship from classmates to sexual partners.
After an intense session with Mio, Megu, and Rina, Anon discovers a shocking truth about his new partners. The three girls reveal that their "gal" personas are a front to hide their country roots and that Anon is actually the first man all of them have ever been with. Now officially designating him as their "sex friend," the girls take his adult collection to study new techniques for their future encounters.
Frustrated by a lack of intimacy, Anon is swept up by Rina, Megu, and Mio, who convince him to skip gym class for a secret rendezvous in the locker room. The encounter becomes even more daring when they are forced to hide in a locker to avoid detection by their teacher, Tanijiri-sensei, resulting in a risky and passionate four-way encounter.
Anon sneaks into the women's locker room to spend his free period with Rina, Mio, and Megu. The girls push the boundaries of their relationship by experimenting with new positions and modifying their clothing for easier access in public places. Just as Anon is reveling in his harem, the group is forced to make a hasty escape to avoid being caught after the school bell rings.