Han Shin-woo met a female college student, Ga-yeon, at a club where he and his classmates went for a graduation party. They met by coincidence when he helped her in getting out of a bad position, and they ended up dating. Shin-woo looked young and naïve, and Ga-yeon is charmed by Han Shin-woo's handsome appearance. Then March came. Shin-woo will be a third-year homeroom teacher at Daehan High School, where he was appointed for the first time, and the class president of class 1 in the third year is Jin Ga-yeon...? "Could it be that you have an older sister?" Shin-woo asked, almost like he was clutching a stick. "...I don't." Ga-yeon's voice replied mixed with tears. / Ga-yeon's voice was filled with sadness as she spoke.