Haruya Iinuma begins as the main antagonist, bullying Tousuke Rokudou and his friends with cruel pranks and intimidation. He possesses a muscular physique, black hair dyed orange on the right side, and wears a red and white jacket over a blue shirt, a red gem necklace, black pants, and brown shoes.

A dramatic shift occurs when Rokudou's supernatural scroll accidentally affects Iinuma's girlfriend, Tsubaki, causing delinquent girls to fall for Rokudou. This event sparks Iinuma to challenge Rokudou to a fight. Though physically outmatched, Rokudou endures a severe beating before calling Ranna Himawari. Witnessing Rokudou's resolve earns Iinuma's respect, transforming him from foe to a close friend and ally. He later learns the truth about the scroll.

Iinuma harbors a passion for motorcycles and ramen, aspiring to run a mobile ramen stand. His motorcycle customization is characterized by impractical, flashy designs frequently deemed gaudy.

Combat-wise, Iinuma ranks among Amori High's strongest fighters, surpassed only by Ranna Himawari and Sayuri Osanada in raw power. This strength makes him a key asset against delinquent gangs.

Relationships define his arc. He maintains a consistent romantic relationship with Tsubaki, forming a secondary couple. His friendship with Rokudou deepens into loyal partnership, driven by recognizing the genuine camaraderie in Rokudou's group—a stark contrast to his past superficial alliances. This loyalty includes defending Rokudou against threats like the Onishima Union. He also maintains friendships with other delinquents, including Takeru Takeyama.

Iinuma's background reveals his initial bullying stemmed from past experiences of weakness, including a childhood fear of thunderstorms. His transformation into a protector reflects an underlying desire for authentic connections, which he discovers within Rokudou's circle.