Futaro Uesugi is seventeen — brilliant and studious, but mocked by classmates for his shy, reserved nature. After a run-in with a newly transferred student named Itsuki Nakano, he discovers he has been hired to tutor her wealthy family. He quickly learns that Itsuki is not alone in needing help: her four quintuplet sisters — Miku, Ichika, Yotsuba, and Nino — are all at risk of failing out of school. His own family's precarious finances leave him no choice but to accept. The girls are skeptical at first. As he helps them pass their exams, Futaro forms a unique relationship with each of them.