Nao Serizawa emerges as a third-year student at Iwatobi Junior High School in *High☆Speed! Vol. 2*, jointly leading the swimming club as co-captain and manager. He mentors first-years Haruka Nanase, Makoto Tachibana, Ikuya Kirishima, and Asahi Shiina. Concurrently serving as library committee president, he frequently interacts with Haruka through shared duties. A retinal detachment disorder necessitates eye surgery during junior high, permanently restricting his swimming capabilities. Post-surgery medical limits cap his pool time at fifteen minutes to protect his eyes, ending his competitive career. He continues supporting the team as a non-swimming manager. His friend Natsuya Kirishima acknowledges the injury’s impact, hoping they might swim together again if medically cleared. This experience redirects his focus toward sports medicine. After junior high, he attends Soufukan High School and later pursues university studies in Tokyo. Enrolled at Oudoukan University (alternately called Sakuradokan University) for sports medicine, he coaches children part-time at a local pool until relocation ends this role. He retains ties to swimming through medical training. Ironically, he becomes the prior tenant of the Tokyo apartment later rented by Haruka Nanase. His personality blends gentleness, patience, and quiet observation with logical problem-solving. He communicates directly on athletic challenges, advising Haruka on developing a biaxial swim style. As a coach, he identifies individual hurdles and crafts tailored improvement strategies, balancing kindness with strict standards. Occasionally forgetful and self-admittedly lazy in some situations, he enjoys maintaining a tropical fish aquarium and watching documentaries or movies with Natsuya. Key relationships shape his path: his foundational bond with Natsuya Kirishima, who provides crucial support during his medical journey, and his mentorship of the junior high swimmers, earning trust through analytical guidance. Later, his university-era encounter with Makoto Tachibana influences Makoto’s shift toward professional swim coaching. Physically, he has droopy lime-green eyes and long periwinkle hair in junior high, later adopting shorter hair and corrective lenses. His height grows from 163cm to 178cm, with lean "type 1" musculature. His symbolic associations include the northern gannet motif and pearl blue image color.