A day starts as usual in Danhwa Girls' High School. But this peaceful and ordinary life totally comes to an end, after lunch time. Blue and Pink bottles of yogurts are served as a meal. All the girls who drink the blue bottles of yogurts begin to turn into boys. The moment So-ah sees the scene, she runs out of the classroom, with astonishment, saying herself, "I have to inform Jae-hee of the fact, ASAP." While hurrying to run, she bangs her forehead on something and falls down. When she is just about to stand up, rubbing her forehead, someone calls her, in a strange voice, with a familiar tone, "Are you all right?" Then, So-ah raises her head and finds that her best friend Jae-hee who has already turned into a man reaches out her hand to So-ah. So-ah asks Jae-hee, "How come… How come you have turned into a man?"