Kotetsu
Kotetsu is a ten-year-old apprentice swordsmith from the Swordsmith Village in Demon Slayer: Kimetsu no Yaiba. As a descendant of the engineer who crafted the Sengoku-era combat automaton Yoriichi Type Zero, he serves as the puppet's current keeper. Although possessing an extraordinarily analytical mind, he initially despairs over his perceived lack of craftsmanship talent. After meeting Kamado Tanjiro, he gains renewed drive, assisting the Demon Slayers and playing a crucial supportive role during the demon attack on his village.
Overview
Kotetsu is a ten-year-old apprentice swordsmith from the Swordsmith Village in Demon Slayer: Kimetsu no Yaiba. As a descendant of the engineer who crafted the Sengoku-era combat automaton Yoriichi Type Zero, he serves as the puppet's current keeper. Although possessing an extraordinarily analytical mind, he initially despairs over his perceived lack of craftsmanship talent. After meeting Kamado Tanjiro, he gains renewed drive, assisting the Demon Slayers and playing a crucial supportive role during the demon attack on his village.
Appearance
Kotetsu wears the traditional Hyottoko mask worn by residents of the Swordsmith Village. Beneath the mask, his actual facial features—including visible cheeks with red spot-like markings and his mouth—are noted to look almost identical to the mask itself. He appears as a short ten-year-old boy dressed in traditional Japanese attire, including kimono and hakama.
Personality
Kotetsu is exceptionally sharp-tongued, headstrong, and unyielding. He holds intense grudges and can be remarkably persistent and reckless when upset, earning him a reputation for eccentricity on par with Haganezuka Hotaru. Beneath his blunt, severe exterior lies a highly observant mind capable of evaluating strengths and flaws. He develops a deep affection for Kamado Tanjiro, genuinely caring for his safety and working tirelessly to help him survive.
Abilities
Kotetsu possesses advanced technical knowledge inherited from his engineer ancestor, enabling him to operate the intricate automaton Yoriichi Type Zero and activate its secret features. His analytical mind allows him to accurately identify flaws and strengths in both crafting techniques and Demon Slayer swordsmanship. He also displays extraordinary mental fortitude, blowing air into a fluid trap to aid a Hashira while suffering a severe abdominal wound. In spin-off material, he demonstrates high mechanical skills by crafting two battle puppets himself.
Background
Born into a lineage of mechanical artisans in the Swordsmith Village, Kotetsu inherited responsibility for Yoriichi Type Zero. Disencouraged by his own perceived limits, he clashed with Tokito Muichiro over the doll's use before Kamado Tanjiro intervened. Outraged when Muichiro damaged the puppet, Kotetsu subjected Tanjiro to a grueling seven-day spartan training session without food or water using the doll's hidden modes, ultimately uncovering an ancient blade inside. During the Upper Rank demon invasion, Kotetsu risked his life to help free Muichiro from a blood demon art, surviving a fatal stab thanks to Kyojuro Rengoku's sword guard kept in his shirt.
Relationships
He forms a deep bond with Kamado Tanjiro after being protected by him, pushing Tanjiro through intense training and entrusting him with the hidden ancestral sword. His relationship with Tokito Muichiro begins with intense resentment over Muichiro's forceful treatment of his mechanical puppet, yet Kotetsu later risks his life to save the Mist Hashira, playing a vital part in unlocking Muichiro's lost memories. He also maintains dynamic, often chaotic interactions with senior swordsmiths Haganezuka Hotaru and Kanamori Kizo.
Trivia
In the official spin-off series Kimetsu Gakuen!, Kotetsu is depicted as a fourth-grade elementary student who is close friends with the Tokito brothers and assists at a relative's pizza shop. In that setting, he displays mastery over arcade claw machines while explaining their mechanics with his signature bluntness. In the animated adaptation's preview segments, his sharp commentary often triggers comedic reactions, driving Tanjiro to run away or thoroughly infuriating Haganezuka.
