Kojirou Sasaki, a legendary swordsman historically defeated and killed by rival Musashi Miyamoto centuries prior, was resurrected through a ritual performed by Takeshi Onimaru. This foul-smelling ritual involved facial slapping by Onimaru's minions, the Hakki, and bound Kojirou to eliminate Yaiba Kurogane. Initially aligned with Onimaru, he wields the enchanted sword "Washing Pole," which extends in length at his command. Though the blade regenerates instantly if severed, its durability proves vulnerable to mystical weapons. A significant weakness is its hypersensitivity to saltwater, including tears, causing uncontrolled elongation upon exposure. Personality-wise, Kojirou exhibits a carefree, confident, and habitually womanizing demeanor, providing recurring comic relief. Despite tendencies toward laziness and occasional cowardice—such as surrendering fights prematurely to avoid injury—he diligently trains in combat and refines his swordsmanship. After Yaiba defeats him using the Thunder Orb's power, Kojirou abandons his assassination mission and joins Yaiba's group against Onimaru. This alliance establishes him as a key fighter in subsequent conflicts, including the battle against the moon princess Kaguya and her forces. Kojirou remains a prominent combatant throughout the series. His swordsmanship relies on precision and adaptability, exploiting his sword's extendable nature for unpredictable attacks. While lacking inherent mystical abilities, his physical prowess and tactical weapon use make him a formidable ally. Evolving from a resurrected antagonist bound by obligation to a voluntary member of the protagonist's team, he contributes significantly to major battles. His flirtatious and occasionally frivolous traits persist, often requiring allies to refocus him during critical moments.