Maruo Nakano is the stepfather of the Nakano quintuplets, having married their mother, Rena Nakano, several years before the story begins. He is a highly accomplished medical doctor and the director of a large hospital, which makes him a wealthy and influential figure. He is characterized by a strict and no-nonsense demeanor, presenting himself as a disciplined, responsible individual who takes his roles as a father and provider very seriously. Maruo is a dedicated workaholic who often puts in long hours at his office and expects strong results from his daughters, particularly in their academic performance. He maintains a calm and realistic outlook, but struggles to express his emotions openly, which can make him appear cold, distant, or intimidating to others. However, beneath this reserved exterior, he genuinely cares for his daughters’ well-being and future, and his decisions, though sometimes harsh, are driven by a desire to secure their success and happiness. His motivation largely revolves around ensuring the quintuplets graduate high school and lead stable, successful lives, which is why he hires Futaro Uesugi as their private tutor despite his initial skepticism. In the story, Maruo serves as an authority figure and occasional obstacle, but his role deepens over time as more of his past and his relationship with the quintuplets are revealed. He is shown to be a caring father who is willing to make personal sacrifices for his family, and his strictness stems from a place of concern rather than coldness. His key relationships are primarily with the five sisters, with whom he has a strained but ultimately loving bond, and with Futaro, whom he initially regards with suspicion but gradually comes to respect. Maruo’s development highlights his journey from an emotionally distant parental figure to one who learns to show his affection in his own awkward way, demonstrating his growth as a father. Notably, he possesses strong intelligence, professional competence, and a keen sense of responsibility, all of which enable him to manage both his demanding career and his household with authority.