The students from a luxurious residential neighborhood, the apartment complexes where the middle class resides, and the underdeveloped residential street all go to the same school and learn in the same classroom. The new semester begins, and Da In, a naïve girl, transfers to school from the countryside. Although she's raised by a single mom, she's a very cheerful literary girl. Due to her pure mindedness, she's bullied by her classmates in the beginning, but Se Chan, a boy from a luxurious town, helps her. Se Chan used to be a bully, but he now hates bullying because of his painful memory. He is confused about whether he helped Da In because he liked her or just hated bullying. The story of how Da In survives in the school where the strata exists in her own cheerful way begins.