Hotaru wears a sunflower-patterned robe and a large, woven hat with hanging floral wind chimes. His head is wrapped in a spotted cloth and his face is concealed by a Hyottoko mask (wooden festival mask), similar to Urokodaki.
During the Swordsmith Village Arc, he is seen with a more muscular build compared to his initial appearance.
Unmasked, Hotaru is revealed to have long, black hair coupled with sharp eyes and distinctly-shaped thick eyebrows.
Hotaru is a rather hot-blooded individual. He seems to show very little care, if any, about anything besides the swords he creates. His passion for swords is so strong that he would be able to speak about them for long periods of time, a trait unique even among the people from the Swordsmith Village.
The same passion that gives him the enthusiasm and extreme dedication in creating swords is also the reason why he is easily enraged (usually in a comical fashion) towards swordsmen that break his creations, especially Tanjiro, no matter the circumstance.
When angry, he usually calms himself down by eating mitarashi dango or by having others pin him down (one method being tickling his sides). It is later on shown that his skills and concentration on swords is so immense that he would lose clients due to his eccentric and asocial behavior and is actually happy that Tanjiro still trusts him in making his swords. His concentration also prevents him from paying any attention to his surroundings when forging a decent blade, even when a demon was attacking him.
Hotaru first appears at Urokodaki's house to deliver Tanjiro's Nichirin Blade after the latter passes the Final Selection. Despite Tanjiro's frequent requests for him to enter the house, Hotaru ignores him and sits outside the door, describing the blade he forged.
After suddenly looking up at Tanjiro, he comments on his red hair and eyes, stating it was good fortune. Excited, Hotaru enters the house while remarking how Nichirin swords would change color and that his sword could turn a bright red, however, after seeing the blade turn jet black, Hotaru shows evident disappointment and gets angry at Tanjiro.
After Tanjiro heals at the Butterfly Estate, he and Inosuke Hashibira greet their swordsmiths but are met with an angry Hotaru charging at Tanjiro with a knife, furious about his broken blade. After chasing him and then calming down, Hotaru and Kozo Kanamori give the swordsmen their blades.
Hotaru appears when Tanjiro comes back from the Rengoku house, enraged over the loss of another sword and chases Tanjiro again.
Abilities and Powers
- His surname contains the kanji for steel (鋼, hagane), a reference to his occupation, and his first name (蛍, hotaru) means "firefly."
- Hotaru's favourite food is mitarashi dango, and he goes out to buy some whenever he loses his temper.
- He hates his first name due to how "cute" it is.