Minami Nanba is a third-year student at Osaka Academy and the head of Dormitory Two, a role that places him in a position of authority over many of the other students. He is known throughout the school as a charismatic and flirtatious figure, often referred to as the top playboy among the student body. His background includes a family that runs a traditional Japanese inn, which is reflected in his natural sense of hospitality and his ability to lead and manage the dormitory with a balance of charm and responsibility. He is also the nephew of Hokuto Umeda, the school doctor, a connection that occasionally draws him into the more personal matters of the students under his care.

Nanba's personality is defined by a confident and outwardly carefree demeanor. He is handsome, self-assured, and highly sociable, frequently engaging in flirtatious banter with girls and maintaining a reputation as a ladies' man. Despite this flashy exterior, he is also surprisingly sensible and dependable. He possesses a strong sense of responsibility toward the students in his dormitory, often mediating conflicts and offering guidance. A past romantic relationship with his tutor, Kanako Tanabe, which ended with her leaving him, is a significant part of his backstory. It is implied that this heartbreak influenced his subsequent playboy behavior, serving as an emotional wall he erected to protect himself from further vulnerability.

His primary motivation is to maintain the stability and reputation of Dormitory Two, which he does with a relaxed but effective authority. He enjoys fostering a sense of community and competition among the dormitories, organizing events and activities to boost morale. On a personal level, he is driven by a desire to move past his own emotional wounds, though he often hides this deeper vulnerability behind his flirtatious persona. In the story, he serves as a dependable senior and a source of comic relief, often clashing humorously with the energetic Shuichi Nakatsu while also acting as a protective older brother figure to the protagonist, Mizuki Ashiya. He is one of the first to discover that Mizuki is a girl, and he chooses to keep her secret, quietly supporting her from the background and offering comfort when she is distressed.

Key relationships include his bond with Mizuki Ashiya, whom he treats with kindness and a protective instinct, acting as a confidant during her difficult moments. He shares a bickering but ultimately affectionate dynamic with Nakatsu, frequently trading jabs with him. His relationship with his uncle, Hokuto Umeda, is marked by Umeda's teasing about his romantic history. He also has a notable connection to the younger student Senri Nakao, who is openly and intensely devoted to him, adding a layer of comedic senpai-kouhai dynamics to his daily life.

Over the course of the series, Nanba shows development by gradually opening up about his past and allowing himself to form more genuine connections. He moves beyond his superficial playboy image, demonstrating a capacity for sincere care and introspection. His role shifts from a purely comedic side character to a more emotionally grounded figure who learns to confront his own vulnerabilities. Among his notable abilities are his strong leadership skills, his popularity and social acumen, and his talent for managing the diverse personalities within his dormitory. It is also mentioned that he was a former winner of the Miss Osaka Pageant during his first year, an achievement he is not particularly proud of, and that in the future he is said to become a model.