Sosuke Yamazaki, a male character introduced in Free!-Eternal Summer-, was born on September 14th under the Virgo sign, aligning with traits like analytical thinking and reservedness. He stands 185 cm in high school, later reaching 186 cm, with a muscular build, teal eyes, and short dark brown hair, often maintaining a serious expression. His long-standing friendship with Rin Matsuoka began at Sano Elementary School and continued through Sano Junior High, marked by competitive swimming. Preferring individual events to avoid shared relay outcomes, Sousuke intensified training after Rin transferred to Iwatobi Elementary, excelling in butterfly until a concealed shoulder injury halted his progress. He pursued physical therapy hoping to recover before reuniting with Rin, but worsening symptoms led him to quit swimming and transfer to Samezuka Academy. At Samezuka, Sousuke joined the swim club, revealing a protective instinct toward Rin. He initially confronted Haruka Nanase as an obstacle to Rin’s Olympic goals, though his stance softened. Despite reluctance toward teamwork, he requested inclusion in Samezuka’s relay to support Rin, prompting a rule change prioritizing passion over speed. His injury eventually forced him from competition, but post-surgery rehabilitation cemented his commitment to swimming’s return. Reserved and stoic, Sousuke appears intimidating yet shows underlying kindness. His analytical, observant nature aids in coaching Aiichiro Nitori through technical struggles. Reliable and precise when supporting valued individuals, he also exhibits skepticism, fussiness over loved ones’ choices, and inflexible viewpoints. Independence breeds emotional detachment; he hides vulnerability, like his injury, to avoid burdening Rin. Denial of personal hardships complicates his emotional interactions. Later, Sousuke attends Seshika Kyoritsu University, working part-time while swimming. After recovery, he joins the Japanese National Swim Team, competing in events like the 4×100 m medley relay. At the Fukuoka Tournament, he swims alongside Rin, Haruka, and Ikuya Kirishima, securing first place. His motif animal is the whale shark, and he frequently gets lost due to a poor sense of direction.