Maruo Nakano is the stepfather of the Nakano quintuplets, having married their mother, Rena Nakano, several years before the story begins. Professionally, he is a highly successful medical doctor who owns and runs a large hospital, making him a wealthy and influential figure. His background as a dedicated physician and businessman shapes his orderly and demanding approach to life. He is characterized by a strict, no-nonsense demeanor, often appearing calm, realistic, and emotionally reserved. This reserved exterior can make him seem cold or overly strict, but underneath it he genuinely cares for his stepdaughters and wants them to succeed. His primary motivation is to ensure the quintuplets receive a proper education and secure a stable future, which is why he hires Futaro Uesugi as their private tutor. Maruo is a workaholic who spends long hours at the office, and he expects measurable results from his daughters. In the story, he serves as a supporting figure whose approval and expectations create a significant external pressure on the quintuplets and Futaro. His role becomes more prominent in the movie, where he appears at the school festival, has a heartfelt moment with his stepdaughter Nino during a hospital visit, and participates in a meeting with the quintuplets’ biological father, helping to resolve lingering family tensions. His key relationships are with his stepdaughters—particularly Nino, who cooks for him in the hospital—and with Futaro, whom he respects as a capable tutor. Maruo’s development is subtle but meaningful: he gradually shows more openness and warmth, such as sharing a lighthearted moment with Futaro during a conference in Hawaii and allowing himself to be more emotionally available. His notable abilities include his medical expertise, his business acumen in running a hospital, and his unwavering sense of responsibility as a provider and guardian.