Kyogai was a member of the Twelve Demon Moons, having held the position of Lower Moon Six. He is also known as Drum Demon (鼓の鬼, Tsuzumi no oni).

Sometime after becoming a Demon, Kyogai was lectured by an unknown individual over the quality of his writings. This person noted that he had become boring, only beating his drum and not leaving his house, and didn't have the skills to teach people. As he left, the individual stepped on one of the Demon's papers, causing an irate Kyogai to kill him.

While still a member of the Twelve Demon Moons, Kyogai slowly lost the ability to eat humans. He was visited by Kibutsuji Muzan, who removed his number due to the Drum Demon having reached his limit. Because of this, Kyogai obsessively began his quest to rejoin the Twelve Demon Moons.

At some point, Kyogai captured Teruko and Shoichi's older brother, Kiyoshi, due to him possessing "rare blood", and took him to the Drum House. Before he could eat him, he was attacked by two other Demons who were also after Kiyoshi's rare blood, suffering an injury that dislodged the drum from his back.

(Source: Kimetsu no Yaiba Fandom)