Kyogai takes on the appearance of a tall, muscular, humanoid like Demon, possessing grayish skin, black hair, razor-like teeth, pointy ears, blood red sclera, deep blue pupils and hidden irises due to it being rolled up to the back of his head. His right eye had the Kanji of the number Six, which signified his position as the Lower Rank Six of the Twelve Kizuki, but due to being deemed too weak he was kicked out of the group and the eye containing his mark was slashed apart by Muzan, leaving behind a white X scar covering the number, signifying that he was no longer one of the Twelve Kizuki. Another one of his unique physical characteristics is that his stomach, shoulders, hips, front chest and back all have drums protruding from them of which he uses for his Blood Demon Art Techniques.
Kyogai is a relatively quiet, nervous and soft-spoken person, despite being a bloodthirsty demon. Rather than scream or roar when annoyed, Kyogai quietly murmurs about whatever is irritating him. He believes it's rude for people to barge into his home and will destroy them for getting in his way. If irritated enough, Kyogai will raise his voice about the nuisance and insult his opponents.
Upon first becoming a demon, Kyogai believed Kibutsuji's blood would make him infinitely stronger. However, when his strength became finite after growing unable to get stronger from eating humans, Kyogai was cast out by his master. Desperate to please Master Kibutsuji and prove the worth of his Blood Demon Art, Kyogai became obsessed with consuming "Marechi", humans with rare blood.
In reality, Kyogai truly desires to be recognized for his talent. He wanted people to love his writing and was devastated when he was told to give up on it. To redeem himself from this humiliation, Kyogai tries to prove himself as a powerful demon in the Twelve Kizuki. This is why he tries so desperately to reclaim his spot. Upon his death, Tanjiro recognizes his talent and allows Kyogai's soul to rest in peace.
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 Kizuki, Kyogai slowly lost the ability to eat humans. He was visited by Muzan Kibutsuji, 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 Kizuki.
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.
As Tanjiro Kamado and his group attended to an injured boy thrown out of the Drum House, Kyogai played the drum on his left shoulder. He passed by the room Tanjiro and Teruko were in, annoyed by the presence of all the intruders in his territory, slapping the drum on his right shoulder when the former attempted to attack him, which changed the orientation of the room. With the arrival of Inosuke Hashibira, the Drum Demon struck his right shoulder again, then once more, his opponent deftly keeping his balance and using the other two as footholds. As Tanjiro and Inosuke quarreled, Kyogai struck the drum on his stomach twice, each time launching a slashing claw attack. He then struck his shoulder drums multiple times, sending his adversaries flying in a disorganized mess. As he stepped in the direction of Inosuke, he, along with everyone else, were transported into different rooms.
Elsewhere, Kyogai obsessed over obtaining "rare blood", his right eyeball rolling forward to reveal that he was once a member of the Twelve Kizuki. He happened upon Tanjiro in the course of his wandering, striking a drum to flip the room upside down, striking another to initiate his claw attack, along with a slew of others to disorientate his opponent. He growled menacingly as Tanjiro got up, despite the combination of new and old injuries.
Continuing to strike his drums to keep his Demon Slayer opponent away from him, memories from the past caused Kyogai to snap, initiating his Rapid Drumming technique and sparking a maelstrom of effects. Apart from a scrape on the chin, this effort was fruitless, Tanjiro evading a collection of manuscripts that fell from a shelf on the ceiling, which surprised the former Kizuki. Despite his continued slash attacks and orientation changes to the room, Kyogai's opponent continued to close on him by using a certain Water Breathing technique. The former Kizuki was further surprised when Tanjiro complimented his Blood Demon Art, before being decapitated. He asked the youth if he really thought his techniques were powerful, which was confirmed, but he was told that eating humans was unforgivable. Fading into oblivion, Kyogai reflected on how Tanjiro had seen the value in all of his work, tears running down his face.
- Right Shoulder: Causes the room he is in to rotate to the right.
- Left Shoulder: Causes the room he is in to rotate to the left.
- Right Leg: Causes the room he is in to rotate forward.
- Left Leg: Causes the room he is in to rotate backwards.
- Navel: Creates a 3 claw-like slash attack.
- Back: Teleports him or other people into another room within his mansion.
- Kyogai was ranked in 20th place as of the first character popularity poll with 130 votes.
- Kyogai is a fan of the Japanese legendarium "The Legend of the Eight Samurai" (
南 總 里 見 八 犬 傳Nansō Satomi Hakkenden?), from this, he was working on his own biography.
- Kyogai's Blood Demon Art is similar to that of the new Upper Rank 4, Nakime albeit her own ability far surpasses his own.
- Similarly to Nakime, Kyogai uses a musical instrument for his Blood Demon Art and was given his epithet due to it.
- In Kimetsu Academy, Kyogai is a music teacher who primarily uses a drum when he holds class. He's often made to do long songs and orchestral pieces, so the students aren't surprised he can't sing the songs in the newer textbooks.