One of his students, Kokonoe Rin, has proclaimed herself to be Daisuke-sensei's girlfriend and is now on the warpath to win him over or get him fired. It is the first day of teaching for Daisuke Aoki and his third grade class. During the course of the day, he learns about the reasons behind Mimi Usa's extended absence from school. Her absence is due to a long-term harassment by the previous teacher. Neither the other teachers nor her parents believed her, so Mimi's only choice was to quit school.