Haruto Sugiyama, a third-year at Ichigo Junior High, holds dual presidencies over the boys' tennis club and the student council. Renowned throughout the school for his maturity, responsibility, athletic skill, and tireless dedication, he commands widespread admiration and even inspires a devoted fan club. His family includes a younger brother, Akihito Sugiyama, who resides in America and possesses an extraordinary IQ of 250. Haruto harbors deep-seated feelings of inadequacy and inferiority when measuring himself against Akihito, forming the core of his personal conflict.

In the first season's latter episodes, the Queen of Nightmares manipulates Haruto's jealousy and insecurity about his brother. This influence temporarily aligns him antagonistically against the main protagonists. During this period, he forms a Dream Partnership with Yuni, a stuffed kitten originally serving the Queen of Nightmares.

His character evolves significantly in *Mewkledreamy Mix!*. Freed from the Queen's control through Yuni and the protagonists' intervention, Haruto confronts and overcomes his longstanding inferiority complex regarding Akihito. Flashbacks depicting his childhood illustrate early contrasts with his brother, foreshadowing his later vulnerability to manipulation. Consistently, his relationships with peers—especially his status as an admired senior and his roles in the tennis club and student council—remain defining aspects of his school life, even throughout his antagonistic phase.