A kind-hearted boy. After his family is slaughtered by a demon, and his younger sister is turned into one, he trains under Sakonji Urokodaki and joins the Demon Slayer Corps so that he can find a way to turn Nezuko back into a human, and avenge his family.
Aside from Water Breathing, he also learns to use Hinokami Kagura during the Mount Natagumo mission. Undergoing further training at the mansion of the Insect Hashira, Shinobu Kocho, he masters Total Concentration, Constant. He then sets off with Nezuko, Zenitsu, and Inosuke on a new mission, joining Rengoku on the Mugen Train.