Maruo Nakano (中野なかの マルオ, Nakano Maruo?) is stepfather of the quintuplets, Ichika, Nino, Miku, Yotsuba, and Itsuki Nakano, and the husband of their late mother, Rena Nakano. He is a successful doctor and businessman who runs a hospital. He hires Fuutarou Uesugi as a private tutor for the quintuplets.

While initially presented as an antagonistic character, he is later revealed to be a responsible and loving father who deeply cares for his daughters and their happiness. His backstory and connection to his daughters are also revealed over the course of the story, making him an important character in the series.