- Japanese Voice Actor: Daisuke Namikawa
- English Voice Actor: Robbie Daymond
- Age: 37
- Manga Debut: Chapter 9
- Anime Debut: Season 1 Episode 5
- Race: Human
- Gender: Male
- Status: Alive
Hotaru was the one who brought the sword of Tanjiro after he passed the final selection exam. He delivered it to the house of Sakonji. Tanjiro invited him to enter the house, but Hotaru refused and instead just explained about the sword.
The sword, according to Hotaru, can change color. When Tanjiro held the sword, which became jet black, Hotaru was disappointed. This was because he was one of the Master swordsmiths of the Swordsmith Village. He was born in the village and learned the craft of forging the Nichirin Sword.
After Tanjiro broke his sword in the fight with Rui, Hotaru repaired the sword and chased Tanjiro with a knife when he brought it back after Tanjiro recovered. When he lost his sword after they fought Enmu and Akaza, Hotaru got furious again.
Hotaru no longer faced Tanjiro after he chipped the sword in his fight in the entertainment district, but he sent an angry letter. When they traveled to the Swordsmith Village to have Tanjiro’s sword repaired, Tanjiro instead found a sword inside a training machine. The sword was 300 years old and was repaired by Hotaru, which is seen to be decisive in battle.
Hotaru wears a woven hat with hanging floral wind chimes. A wooden festival mask or Hyottoko mask conceals his face. As the series progresses, he becomes more muscular. He always wears his mask, and when he takes it off, it is shown that he has long black hair, sharp eyes, and eyebrows with a distinct shape.
He wears a haori that has a sunflower pattern. After the attack at the Swordsmith Village, he possesses deep scars all over his body. He also lost his left eye from the attack and has an x-shaped scar on his face.
Hotaru only cares about what happens to the sword. It was shown on several occasions how he would get angry when the sword would get broken. He would get angry over the damage to the sword. He is capable of talking for hours about swords.
This trait is true for every person who resides in the village. His dedication to creating swords is so extraordinary that he would get angry when his sword would be damaged. Regardless of whether the sword was used to defeat demons, he wanted the swords to be in top shape.
When he gets angry, he calms himself by eating mitarashi dango. If eating dango does not work, he would ask someone to pin him down or tickle him. He has eccentric and asocial behavior. These behaviors are the reason why he would lose clients.
He forgets about his surroundings and ignores everyone when he forges a sword. When Tanjiro expressed his trust in him to still forge his sword despite his attitude, Hotaru was happy to forge his sword.
Hotaru is an expert in Tantojutsu, a special ability he has. He only displays this ability when he chases Tanjiro for destroying his sword. Despite being a master at forging a sword, he does not display any special ability.
He could not even wield the sword. He would train hard for stamina and strength to forge a better sword. His ability to forge exceptional swords, like the 300-year-old sword from Yoriichi Type Zero, proves that he is one of the Master swordsmiths of the Swordsmith village.