Rei Ryugazaki began at Iwatobi High as a track and field athlete focused on pole vault, valuing sports primarily for their theoretical beauty and logical execution. His analytical nature caused frequent overcalculation during performances, overshadowing the inherent joy of athletics. Persistent persuasion from classmate Nagisa Hazuki led him to reluctantly observe the swim club during a joint practice with Samezuka Academy. There, his inability to swim surfaced embarrassingly—he could float but sank immediately when attempting strokes. Witnessing Haruka Nanase's freestyle swimming shifted his perspective; its beauty transcended pure theory and compelled him to join the Iwatobi Swim Club despite initial reluctance. Driven by appreciation for aesthetics and precision, he approached swimming methodically, evaluating variables like distance and trajectory. Early struggles were significant; he managed only the butterfly stroke after discovering an unexpected affinity for its rhythm during a week-long challenge to learn swimming. This specialization secured his role as the team's butterfly swimmer. Training involved reliance on kickboards and pull buoys, supplemented by secret practice to overcome limitations. His rigid mindset initially blocked his ability to experience swimming's freedom—a point Haruka emphasized by noting water's resistance to pure analysis. Interpersonal growth paralleled athletic development. His formal speech and social awkwardness made him feel like an outsider among teammates with shared histories, though deep bonds gradually formed. Nagisa frequently manipulated or pranked him, provoking emotional reactions that disrupted his usual composure. He held profound admiration for Haruka's swimming and later accepted guidance from Rin Matsuoka, who taught him all competitive strokes. Rei expressed gratitude for this mentorship by baking cookies for Rin. Advancing to his third year, he assumed swim club captaincy after Makoto Tachibana's graduation, leading the team to nationals. There, he reunited with elementary school acquaintance Asahi Shiina and achieved personal best times. Beyond swimming, he excelled academically in mathematics and chemistry but struggled with art and music. Hobbies included reading, running, and calculating, reflecting intellectual inclinations. Personal quirks involved a preference for sushi and foods deemed beneficial for the body, avoidance of unhealthy options, and a dislike for supernatural topics like UFOs. He experienced motion sickness and maintained family traditions such as pairing melon bread with barley tea. Post-high school, he enrolled at Shimorou Academy University alongside Aiichiro Nitori, continuing athletic and academic pursuits. Physically, he featured distinctive red hexagonal glasses and grew from 152 cm in middle school to 179 cm by his third year. Athletic development resulted in defined musculature classified as "hard" compared to peers. A butterfly motif symbolized his transition from track to swimming, representing transformation and non-aquatic origins. This motif extended to his swimming style and the broader narrative theme of evolving beyond theoretical constraints into embodied athletic expression.