Hotaru Haganezuka is a master swordsmith affiliated with the Demon Slayer Corps, residing in the secret Swordsmith Village. At thirty-seven years old, he hails from the esteemed Haganezuka clan, known for their craftsmanship. His temperament was so extreme in his early childhood that his parents suffered a mental breakdown, leading the village chief, Tecchin Tecchikawahara, to raise him instead. The chief also gave him the name Hotaru, which means firefly, a name Haganezuka personally finds too cute and dislikes. He wears a traditional Hyottoko mask that conceals his face, a spotted headscarf, and a straw hat from which several floral wind chimes hang, a relic from a childhood calming mechanism. Underneath his mask, he has sharp eyes, thick eyebrows, and long dark hair. During the Swordsmith Village Arc, after rigorous mountain training and a subsequent attack by the Upper Rank demon Gyokko, his body becomes notably more muscular, and he sustains severe injuries including a blinded left eye and deep scars across his face and body.

Haganezuka possesses a hot-blooded and volatile personality that borders on socially destructive. He is self-centered, often talking over others, and has a reputation for reacting with explosive fury whenever a blade he has forged is damaged, broken, or lost. This has historically caused him to be disliked by swordsmen and frequently removed from his assignments. Despite this, his dedication to the craft of sword making is obsessive and absolute. He pours tremendous pride into every blade and expects the wielders to treat them with the same reverence. His anger is often portrayed comically; he is known for chasing Tanjiro Kamado around with kitchen knives for hours after his swords are broken. However, these rages have specific antidotes, including eating mitarashi dango or being tickled under the arms, which renders him limp and docile. While he presents a fearsome exterior, especially toward those who misuse his work, he harbors a deep and unspoken respect for the Demon Slayers who risk their lives and is secretly pleased when a slayer like Tanjiro continues to trust his skills.

Haganezuka was assigned to forge the Nichirin Blade for Kamado Tanjiro after the Final Selection. He arrived at the home of Sakonji Urokodaki, presented the sword, and expressed great hope that it would turn red, a color he favored. When the blade instead turned black, he became angry with Tanjiro. This pattern repeated as Tanjiro broke his blade fighting the Lower Rank demon Rui, lost it on the Mugen Train, and severely damaged it in the Entertainment District. After the third incident, Haganezuka’s fury reached a peak; he sent Tanjiro a curse-laden letter stating he would refuse to forge another blade and then disappeared from sight. In truth, he retreated to the mountains for intense physical training, driven by a desire to forge a stronger and sharper blade that could help Tanjiro survive his fierce battles. This action reveals his true motivation: he is not simply enraged by the damage to his art, but is genuinely committed to the well-being of the slayer who wields his swords. His role is therefore critical as the provider of the essential weaponry, and his personal arc in the Swordsmith Village demonstrates a shift from pure frustration to a dedicated, self-sacrificing partnership with Tanjiro.

Within the story, Haganezuka’s key relationships are primarily with the village chief and with Tanjiro. He was raised and trained by Chief Tecchin Tecchikawahara, who understands his personality and often mediates on his behalf. His relationship with Tanjiro Kamado is the most central; it begins with anger and mutual frustration but evolves into a bond of unspoken mutual respect. Tanjiro consistently chooses Haganezuka as his swordsmith despite his terrifying temper, which secretly makes Haganezuka very happy. He overhears Tanjiro defending the importance of swordsmiths to the Hashira Muichiro Tokito, a moment that deeply moves him. He also has a professional relationship with fellow swordsmith Kozo Kanamori, who is one of the few people capable of physically calming him down by tickling him. His direct interaction with Upper Rank Gyokko showcases his defining development as a character; while Gyokko attacks the village, Haganezuka focuses entirely on polishing a legendary rusted blade he retrieved from the Yoriichi Type Zero training doll. Even after having an eye gouged out and his workspace destroyed, he continues his work, demonstrating a level of concentration and dedication that even a demon finds terrifying. After the battle, he finishes polishing the blade and delivers it to Tanjiro at the Butterfly Mansion, explaining its history and demanding a lifetime supply of mitarashi dango as compensation, a gruff way of ensuring Tanjiro lives long enough to pay him back.

Notable abilities distinguish Haganezuka as more than a simple craftsman. He is a master of the Haganezuka family’s traditional and grueling polishing technique, a method so rigorous that it has historically led to the death of swordsmiths from exhaustion. He demonstrated the ability to work for three days and three nights without sleep, maintaining intense focus. His decision to undergo mountain training granted him a superhuman level of physical strength and stamina, evidenced by his dramatically transformed muscular physique. This allows him to withstand the physical toll of his craft and even survive direct attacks from an Upper Rank demon. While he is not a combatant, his physical prowess is such that he can chase a trained Demon Slayer for hours. His most fearsome ability, however, is his indomitable will and concentration; when focused on his craft, he becomes completely oblivious to external threats, including deadly poison and life-threatening injuries, ignoring them entirely to complete his work.