Momotarō Mikoshiba, a second-year Samezuka Academy student and younger brother of ex-swim captain Seijūrō Mikoshiba, thrives on attention with his boisterous, exuberant personality. His loud, confident demeanor clashes humorously with his lean, boyish frame, which lacks his brother’s muscularity but retains a youthful charm. Initially disinterested in competitive swimming, he joins the team after relentless persuasion from Rin Matsuoka, eventually specializing in backstroke. As part of Samezuka’s relay quartet with Rin, Sousuke Yamazaki, and Aiichirō Nitori, his fiery drive for victory surfaces through gritted expressions and clenched fists—a raw, gemstone potential awaiting polish. His comedic pursuit of Rin’s sister, Gou Matsuoka, underscores a girl-crazy streak mirroring his brother’s fondness for flirtation. Playful banter with teammates, particularly Rin, balances his brashness, cementing his role as both a spirited jester and a vital relay asset. Dubbed “The Sea of Japan’s Sea Otter” for his agile strokes, his nautical-themed attire—casual uniforms and varied swimwear—echoes his aquatic persona. Though his backstory remains unexplored, his growth pivots on evolving from a hesitant recruit to a linchpin in Samezuka’s relay strategy, fueled by budding teamwork and rivalry. Familial ties to Seijūrō linger as subtle expectations, yet his narrative prioritizes individuality over comparisons. Dynamic clashes with Sousuke, contrasting their rivalry styles, deepen team chemistry, highlighting Momotarō’s unrefined zeal as both a liability and a catalyst for camaraderie.