Seijuurou Mikoshiba is a prominent swimmer in the *Free!* franchise, with significant development in *Dive to the Future*. As captain of Samezuka Academy's swim team during high school, he commanded attention through leadership, a towering height of 187 centimeters (later 188 cm), a weight of 77 kilograms, and a muscular build optimized for endurance swimming. His freestyle expertise centers on long-distance events, leveraging powerful strokes, substantial lung capacity, and relentless stamina over speed or technique—traits that secured competition records. He also demonstrates breaststroke proficiency, a skill he deliberately refines during college. After high school graduation, he passes the Samezuka captaincy to Rin Matsuoka, a teammate and friend he mentored and respected. Attending Todoroki University on an athletic scholarship, Seijuurou appears as a senior swim team member in *Dive to the Future*, supporting juniors like Haruka Nanase and Asahi Shiina. His college journey includes a pivotal setback: defeat against professional swimmers at a national meet prompts a year-long competition hiatus. This period of self-reflection and training reignites his potential, inspired by peers’ performances at the Fukuoka meet. He then dedicates himself to mastering breaststroke, diversifying his capabilities. Personality blends cheerful enthusiasm with deep responsibility. He exhibits straightforwardness, dependability, and playful moments yet maintains strict leadership standards. His romantic interest in Gou Matsuoka often distracts him. Valuing camaraderie and mentorship, he consistently supports former teammates during critical meets post-graduation. Family dynamics include a close but competitive bond with younger brother Momotarou, who joins Samezuka’s swim team and shares an affinity for Gou. Seijuurou also has a younger sister, Isuzu, who captains her high school swim team at an institution linked to Todoroki University. Externally, he fosters a friendly rivalry with Tsubasa Hoshikawa, captain of Shirokami Academy University’s swim team, facing off in swim meets and school festival challenges. Seijuurou evolves from a high school captain focused on immediate goals to a collegiate athlete confronting broader competition. His arc encompasses setbacks, a transformative hiatus, and unwavering commitment to peers while relentlessly expanding his athletic horizons.