When going back home from school in the usual train line, Miyu's breasts are groped by a train molester. Shun, her classmate, appears and saves her. He walks her home and teases her about the chikan groping her breasts. He also kisses her.

Miyu runs off to home. The truth is, however, that the train incident was all a cunning trap plotted by Shun. Back home, Miyu regrets having her first kiss stolen. Then, Kou, her childhood friend, appears and, due to Miyu losing her key, takes her to his home. There, Miyu confess her first kiss was stolen. However, Kou tells her they have already kissed, so it was not her first kiss.... That night, Kou takes Miyu's virginity.

The next day at school, Shun apologizes and invites her home. Miyu accepts, not knowing is a trap. There, Shun drugs her and trains her as sex slave. She resists it at first, but after that day, when she remembers that, she starts masturbating. Did she actually like it, and does she want more? What about Kou?