Aoki Daisuke, a 23-year-old schoolteacher, has a major problem. Kokonoe Rin, one of his bright third-grade classmates, develops a crush on him! Indeed, the naughty Rin has declared herself Daisuke-lover sensei's and is now on a mission to either win him over or fire him... whatever happens first! But that isn't the end of Daisuke's worries; he now needs to figure out what happened to Usa Mimi, Rin's buddy who has yet to attend school.