High-school student Fuutarou Uesugi is an academically gifted student that leads a difficult life—his mother has died, he has no friends, and on top of all that, his father has incurred a large amount of debt.

An opportunity presents itself when the rich Nakano family transfers to his school. Fuutarou is promptly hired as a highly paid tutor. However, much to Fuutarou's dismay, he discovers that his five charges—identical quintuplet sisters of varied personalities—have no interest in studying at all and have abysmal grades. Some of the quintuplets are against having Fuutarou, whom they view as a stranger, in their apartment, but Fuutarou's diligent tenacity gradually convinces those girls to accept him and to improve their grades.

Throughout the series, Fuutarou develops special relationships with each of the quintuplets. Through a flashforward, it is revealed that he eventually marries one of them, but her true identity is only revealed near the end of the series.