Mr. Suminoe is the patriarch of the blended Suminoe family, father to his biological son Keita and stepfather to his wife's twin daughters, Ako and Riko. He presents as a middle-aged man with black hair and glasses, his exact age undefined.

He displays eccentricity and permissiveness regarding his children's unconventional romantic entanglements, actively encouraging Ako and Riko's pursuit of Keita. While he advocates for exploring relationships to find "a special someone," he simultaneously emphasizes loyalty, instructing that men should gently reject unwanted advances and never cheat. His own actions, however, contradict this stance, exemplified by carelessly leaving a salirophilia-themed adult video (involving a fetish for defilement with sweets) in his home office, later discovered and used by Riko to influence Keita. His permissiveness extends to placing bets with his wife regarding Keita's potential choice between the sisters.

He frequently delivers grandiose speeches about masculinity, urging Keita to follow his instincts without overthinking. Despite this, he is ultimately submissive to his wife, whose interventions temper his behavior during sibling conflicts. He is deeply devoted to her, their relationship marked by ongoing physical intimacy.

His parenting involves direct intervention in the siblings' conflicts. When a young Keita expressed a desire to marry both sisters, he pragmatically explained polygamy's illegality, inadvertently dissolving Keita's childhood infatuation. His advice often blurs ethical boundaries, reflecting a belief in instinct-driven decisions over societal norms.

Across all media—manga, TV series, and OVAs—he consistently functions as a provocateur, enabling the siblings' taboo dynamics while maintaining a comically morally ambiguous presence. His background lacks detailed exploration, and his character undergoes no significant development or changes throughout the series.