Born on Tsushima Island and raised by pirates without knowing his parents, Yusuke Mizuhara harbored curiosity about mainland Japan. He stowed away on a trade ship during a Joseon Korean invasion of Tsushima. A typhoon destroyed the ship, but he survived by clinging to debris and washed ashore near Kyoto. Exhausted and starving, he received aid from a blacksmith named Tetsuoka, who offered him shelter and apprenticeship in exchange for help. Yusuke initially disliked the forge work but persevered, discovering an innate talent for sword-smithing. His renowned blades lifted Tetsuoka and Tetsuoka's daughter Konitsu from poverty. Tragically, Yusuke returned home to find them killed by a demon. The Flame Hashira, Enjūro Rengoku, arrived too late to save them but defeated the demon, motivating Yusuke to become a Demon Slayer. Enjūro referred him to a trainer. Yusuke's familiarity with swords and endurance from forge work accelerated his combat training. He met fellow trainee Yuri Hanae, who reminded him of Konitsu. During a Demon Slayer gathering, Yoriichi Tsugikuni demonstrated breathing techniques. Unable to master Yoriichi's style, Yusuke adapted it into a fluid, acrobatic form matching his flexibility, naming it Water Breathing (水の呼吸, Mizu no Kokyū). He became the first Water Hashira of the Demon Slayer Corps, with Yuri later appointed as the Flower Hashira. Yusuke typically displayed a stoic, unbothered expression and reserved demeanor. He adhered strictly to the Demon Slayer Corps' code, showing intolerance toward those who disregarded limitations or wasted their lives. Ruthless against demons, he showed pragmatism by offering painless deaths to surrendering demons via his self-invented Fifth Form: Blessed Rain After the Drought. A strong sense of justice coexisted with protectiveness toward close friends like Yuri, though he prioritized duty over personal ties. His personality hardened after Tetsuoka and Konitsu's deaths, making him emotionally distant until Yuri confronted him, restoring some earlier traits while retaining bluntness and a short temper. Physically, Yusuke was tall and muscular with sharp navy blue eyes and long, wavy black hair tied in a ponytail. He maintained his hair with camellia oil after Konitsu and Yuri complimented it. His standard attire included a blue cloud-patterned kimono, black hakama pants, a white waist sash, and zōri sandals. As the creator of Water Breathing, he mastered ten techniques. His swordsmanship emphasized fluid, adaptable motions, leveraging joint flexibility for acrobatic maneuvers. He awakened a Demon Slayer Mark during the Sengoku Period—a blue, water-like design on his left cheek—enhancing physical and Breathing Style capabilities by 100-fold. He temporarily manifested a Bright Red Nichirin Sword and accessed the Transparent World during intense battles. Before becoming a Hashira, he killed a demon using forging tools and molten metal. He forged his own deep blue Nichirin katana with a hexagonal handguard, engraved "Destroyer of Demons" (惡鬼滅殺, Akki Messatsu). He also reforged the Mist Hashira's rusted blade, vowing never to repeat the task due to its difficulty. Yusuke viewed other Hashira variably: he respected the Flame and Stone Hashira, tolerated the Mist and Thunder Hashira, and clashed frequently with the hot-tempered Wind Hashira, Takeshi Hayate. He maintained a complicated bond with Yuri Hanae, whom he knew since childhood or training. He served as Water Hashira for 31 years, participating in key battles against archdemons like Kanki and Izanami. During these conflicts, he sustained severe injuries, including losing an arm, but persisted with tactical intellect and indomitable will.