Muichirō Tokitō, son of a woodcutter and his wife, lived with his twin brother Yuichirō. At age ten, their mother succumbed to illness; their father later perished falling from a cliff while seeking medicine, leaving the twins orphaned and isolated in their forest cabin. Initially compassionate and optimistic like his father, Muichirō contrasted his brother Yuichirō, who adopted a cynical belief in self-preservation over aiding others. Amane Ubuyashiki, wife of the Demon Slayer Corps leader, sought to recruit the twins as descendants of the first Demon Slayer, Yoriichi Tsugikuni, but Yuichirō refused. During a demon attack, Yuichirō shielded Muichirō, sustaining fatal wounds. Enraged, Muichirō killed the demon with makeshift tools, only to return to his dying brother. With his final breath, Yuichirō revealed "Mu" in Muichirō's name signified "infinity" and limitless potential, not "nothingness." This trauma erased Muichirō's memories and suppressed his original personality beneath unexpressed anger. Amane Ubuyashiki later discovered him near death and brought him into the Demon Slayer Corps. Within two months of training, Muichirō achieved the rank of Mist Hashira, matching Gyomei Himejima's speed. He displayed an air-headed, detached demeanor, often lost in thought and indifferent to others. He operated solely on cold logic, exhibiting arrogance like belittling swordsmiths and dismissing their work. His uniform featured loose, kimono-like sleeves and omitted calf wrappings, designed to obscure his movements in combat. Despite his aloofness, he showed deep respect for Corps leader Kagaya Ubuyashiki. A pivotal shift occurred during the Swordsmith Village Arc against Upper Rank Five demon Gyokko. Near death, Muichirō awakened his Demon Slayer Mark—red, mist-like patterns amplifying his strength, speed, and reflexes—and regained his lost memories. This restored his original empathy and kindness, prompting him to thank Tanjiro Kamado for indirectly helping him reconcile his past. He became emotionally open, forming friendships and showing concern for others, like saving young swordsmith Kotetsu despite prior mistreatment. In the Infinity Castle Arc, Muichirō battled Upper Rank One, Kokushibō, alongside Sanemi Shinazugawa, Genya Shinazugawa, and Gyomei Himejima. During this fight, he unlocked the Transparent World, perceiving muscle movements and blood flow, and manifested the Bright Red Nichirin Blade to hinder demon regeneration. Despite catastrophic injuries—losing an arm, both legs, and half his torso—he utilized "Omnipresent Rage" to maintain focus. His final act involved pinning Kokushibō with his crimson blade, enabling Gyomei to strike a decisive blow. This sacrifice directly contributed to Kokushibō's defeat but caused Muichirō's death shortly after from his wounds. His combat prowess centered on Mist Breathing, a swordsmanship style comprising seven forms. He personally created the seventh form, "Obscuring Clouds," using erratic tempo shifts to disorient opponents. His physical strengths included extraordinary speed—capable of instantly decapitating 10,000 targets—and immense endurance, fighting through severe poisoning and limb loss. As the youngest Hashira, his legacy included a pivotal role in weakening Muzan Kibutsuji's forces. During the Hashira Training Arc, Muichirō participated in preparing lower-ranked Demon Slayers for the final conflict with Muzan. He oversaw movement-based training focused on agility and evasion. His cooperative and focused interactions here reflected his post-memory restoration personality, contrasting his earlier detachment and underscoring his commitment to the Corps' strength before the ultimate battle.