Sōjirō Yagyū, known as Sōjirō the Willow Sword, is a Visitor from Earth's Japan, the last practitioner of the Yagyū clan's swordsmanship. His defiance of physics through swordsmanship propelled him to another world. He appears as a short, slim young man with dark brown hair in a rough ponytail, reptilian-like bulging eyes, and a hunched posture, typically wearing a red tracksuit top draped loosely over his shoulders and carrying a dull practice sword. A battle fanatic driven solely by seeking powerful opponents, Sōjirō displays no fear and ignores social conventions or relationships. He operates with a focus on personal freedom, living without regrets and remaining oblivious to non-combat matters. This detachment caused survival difficulties before partnering with Yuno the Distant Talon as his guide. Despite his aloofness, he sometimes shows concern, urging Yuno to flee during battles or rescuing her from captivity. He gradually develops limited empathy, experiencing genuine terror during his fight with Ozonezma and reflecting on how this mirrored Yuno's fears. He hails from a post-apocalyptic Earth devastated by ecological collapse and warfare. He mastered the transcendent Yagyū Shinkage-ryū swordsmanship instinctively, achieving legendary status. He destroyed the largest recorded golem in history—a mountain-sized construct with arms thicker than city spires—using only a practice sword by exploiting its structural weaknesses to shatter its core, cementing his reputation as an unparalleled swordsman. His combat abilities include supernatural intuition and analytical prediction, instantly identifying fatal weak points. He moves at supersonic speeds, intercepting attacks faster than sound and deflecting projectiles like musket bullets. His techniques encompass air manipulation, sword beams, and "Muto-Dori" (sword-disarming martial arts). He wields a non-magical practice sword yet achieves absurd cutting power, slicing through nigh-invulnerable materials like celestial charsteel armor, and possesses superhuman endurance for prolonged battles. He entered this world saving Yuno from golems destroying Nagan Labyrinth City, subsequently destroying the Dungeon Golem in exchange for her packed lunch. Aware of Yuno's animosity and her plan to find someone capable of killing him, he accepts her guidance to Aureatia seeking stronger foes. He joins the conflict against the New Principality of Lithia under Aureatia's Twenty-Nine Officials, undertaking missions like assassinating Taren the Punished. During this conflict, he battles adversaries such as Shalk the Sound Slicer—drawing due to Shalk's imperceptible speed—and infiltrates Lithia alone, encountering Nihilo the Vortical Stampede and cleaving part of her mech's head. In Lithia, he rescues Yuno from Dakai the Magpie, another Visitor. During their duel, Sōjirō anticipates Dakai's counterattacks and exploits his blunt practice sword to land a fatal blow. Post-war, he continues traveling with Yuno, acknowledging his inability to understand her emotions but accepting her guidance. He later serves as a bodyguard for Elea the Red Tag, demonstrating impatience with lesser threats like a wurm. His development includes gradual introspection, discussing his world's destruction with Yuno and participating in the Sixways Exhibition. There, he faces Ozonezma the Capricious, experiencing true terror for the first time and relating it to Yuno's fears.