Kōsuke Iwana, once a disciplined baseball player, turned to surfing after an elbow injury forced him to abandon his initial athletic career. He channels his serious athletic focus into rigorous surfing training, never missing practice as he strives to reach the top. His striking appearance features near-black hair cut shorter at the back while cascading longer near his jawline, paired with distinctive bright red eyes. He surfs wearing a mixed red, gray, and black wetsuit, riding a red surfboard emblazoned with a black shark head design featuring an open mouth.

Driven by fierce determination and competitiveness, Iwana often pushes himself relentlessly, bordering on overtraining. This intense drive coexists with a noticeable social awkwardness, particularly around women. His character evolves to form a significant bond with Yūta Matsukaze, establishing a profound mutual trust.

His favorite food is cream puffs. The surname Iwana combines the characters for "stern/strict" (厳) and "name/reputation" (名).