Kotetsu is a young supporting character from the Swordsmith Village, introduced during the Swordsmith Village Arc of Demon Slayer: Kimetsu no Yaiba. He is a ten-year-old boy of short stature with pale skin and black hair, which he typically wears tied in a low ponytail. His attire consists of a striped yukata, and he always wears a Hyottoko mask that fully conceals his face; it is noted that his actual face bears a strong resemblance to the mask. The back of his yukata displays the kanji for Hyottoko, connecting him to that traditional folk figure.

Kotetsu is an apprentice swordsmith and a descendant of the craftsman who built the mechanical battle doll known as Yoriichi Type Zero. This doll was created centuries ago to train demon slayers, and Kotetsu’s family has been its caretaker ever since. After his father’s death, Kotetsu became the sole keeper of the knowledge required to maintain the doll. This responsibility weighs heavily on him, as he has not yet mastered the repairs and lives in constant fear that the doll might break beyond his ability to fix.

In terms of personality, Kotetsu is kind and energetic, but also very frank and sometimes blunt. He can be hot-headed and insecure, easily discouraged by his own perceived limitations. Despite his rough edges, he genuinely wants to help those around him and is deeply passionate about his work. His analytical mind gives him a sharp eye for both craftsmanship and swordsmanship, which also makes him acutely aware of his own shortcomings.

Kotetsu’s role in the Swordsmith Village Arc is primarily that of a guide and helper. He introduces Tanjiro Kamado to the Yoriichi Type Zero doll, which becomes an important training tool. His initial grief and fear about maintaining the doll begin to fade after Tanjiro encourages him to keep trying, inspiring Kotetsu to persevere. Later in the arc, during the attack by the demons Hantengu and Gyokko, Kotetsu is attacked by a goldfish demon but is rescued by the Mist Hashira, Muichiro Tokito. Despite his earlier resentment toward Muichiro for having broken part of the doll in the past, Kotetsu asks the Hashira to save the swordsmiths Haganezuka and Kanamori, showing his concern for others. His relationship with Muichiro evolves from initial bitterness to gratitude.

Kotetsu also has a notable dynamic with the hot-tempered swordsmith Haganezuka; he is not afraid to taunt the older man, once throwing pebbles at him and insulting his temper and lack of social skills, though this is done in a childish, spirited manner. Throughout the arc, Kotetsu survives the demon attacks and continues to live in the village.

Kotetsu does not possess combat abilities or a breathing style. His strengths lie in his craftsmanship knowledge, his keen observational skills, and his dedication to preserving his family’s legacy. He represents the next generation of swordsmiths who support the Demon Slayer Corps from behind the scenes, and his character arc highlights themes of perseverance, tradition, and personal growth in the face of fear and responsibility.