Kojiro Sasaki, a resurrected swordsman slain by Musashi Miyamoto four centuries earlier, is reanimated via a grotesque ritual involving foul-smelling components and facial strikes under Onimaru’s orders. Initially bound by dark magic to assassinate Yaiba Kurogane, he defects upon losing to Yaiba’s Raijin Sword, shifting from antagonist to an unpredictable ally within the protagonist’s circle. His rivalry with both Yaiba and Musashi fuels his relentless drive to prove his martial supremacy. Armed with Monohoshizao, a katana whose blade extends infinitely on command, Kojiro exploits its reach to target enemy blind spots. However, the weapon falters under saltwater exposure—whether from oceanic environments or emotional tears—causing erratic, uncontrollable elongation. Though durable enough for strategic skirmishes, it remains outmatched by other enchanted blades in prolonged clashes. Despite his comedic tendencies as a flirtatious troublemaker, often reined in by exasperated allies, his combat ingenuity and swordsmanship remain formidable. Kojiro engages in critical battles against Onimaru’s demons, interdimensional invader Princess Kaguya, and the serpentine Yamata no Orochi. His alliance with Yaiba’s group cements during the Kaguya conflict, where he aids in merging the Raijin and Devil Wind Swords to unleash the "Wave of Wind Thunder" technique. Transitioning from self-serving mercenary to grudging collaborator, he continues pursuing personal glory in tournaments and clandestine fights, such as the Pyramid and Oda Nobunaga Tournament arcs, wielding Monohoshizao’s adaptability to outmaneuver foes. His character maintains narrative consistency across adaptations, anchored by his resurrection lore and rivalry with historical peers. No expanded backstory or spin-off explorations alter his core role as a roguish, ambition-driven swordsman navigating loyalty and vengeance within the main storyline’s supernatural conflicts.