Haruo Minami is the eldest son of the other Minami family, a separate household from the main three sisters who are the focus of the series. His name follows his family’s naming pattern, with the character for spring, "haru." He is of at least high school age, though it is unclear if he is still a student or if he has since entered the workforce or college. Physically, he is depicted with neck-length blond hair and gray eyes. Despite being the eldest brother, his physical strength is underwhelming, notably lacking compared to his younger brother Natsuki.

In terms of personality, Haruo maintains a calm and composed demeanor, which stands in stark contrast to the more chaotic and expressive personalities of his brothers. He does not share their overt concern regarding the effects of their behavior on their younger sister, Touma. This detached calmness, however, masks a more troubling set of motivations. In the anime, particularly in Minami-ke: Okaeri, he exhibits behavior strongly suggesting a sister complex, or siscon. He refuses to accept the possibility of Touma having any romantic relationships and is shown fondling a picture of her. It is also revealed that when Touma was very young, Haruo gave her a manga about "loving your brother," which another character, Akira, implies may have influenced Touma's own unusual development.

Within the narrative, Haruo's role is tied closely to his family's household. He is a counterpart to his brothers, filling the position of the eldest sibling. His key relationship is with his sister, Touma, towards whom his possessive and inappropriate behavior is directed. He also interacts with his brothers, contrasting with their more outwardly flustered reactions to the family's unusual dynamics. Despite being the calm one, he seems to be in a state of denial about the adverse effects his and his brothers' lifestyles are having on Touma. His character does not undergo significant development, remaining a static figure defined by his composed exterior and his concerning fixation on his sister. A notable ability, or rather lack thereof, is his underwhelming physical strength, which is highlighted when he is sent flying a considerable distance by a mere pat on the shoulder from his brother Natsuki. Like his brothers, Haruo is not seen or mentioned in the second anime season, Minami-ke: Okawari.