Kiriya Ubuyashiki

Kiriya's docile and emotionless disposition during Final Selection. During his first appearance as an attendant of Final Selection, Kiriya portrays himself to be polite, competent, and somewhat emotionally detached, having calmly and politely greeted the trainees in sync with his sister and professionally explaining the details regarding the test. He was unfazed when Genya Shinazugawa roughly manhandles his sister before being stopped by Tanjiro Kamado, only sarcastically asking if they were finished. Later, upon his father, mother, and older sisters' deaths, Kiriya shows an entirely different side to himself, displaying his capabilities as a leader. He immediately jumps into his new position and organizes himself to monitor and command the Demon Slayers on their attack against Muzan Kibutsuji and the remaining Twelve Kizuki, despite just losing half of his family and not even properly having the time to mourn them. He shows more mental fortitude and emotional strength in comparison to Kanata, who momentarily broke into tears in grief. Kiriya is also shown to have had complete confidence in the Demon Slayers he commanded, as he refused to send Tanjiro and Giyu Tomioka to fight Upper Rank One, believing that the combined efforts of Gyomei Himejima, Muichiro Tokito, and Sanemi and Genya Shinazugawa would be enough to defeat him. Despite his mental fortitude, Kiriya is not immune to breaking down mentally. However, once his plan results in the slaughter of many Demon Slayers after Muzan emerges from his flesh cocoon, Kiriya breaks under the severe stress and stops giving orders, believing that not only would Muzan win and all of their sacrifices and efforts would be in vain, but that he would be solely responsible for it. He is able to pull himself back together after Kuina slaps him in the face to shock him out of his catatonic state and encourage him. Although Kiriya would continue to be heavily stressed in the remaining fight against Muzan, and despite even being injured by his shockwave, he perseveres and continues taking charge even as Muzan is burning in the sunlight. In the aftermath of the Corps' disbandment after Muzan had been defeated, Kiriya is able to live out his life as a normal child, no longer the head of the Demon Slayers. In particular, when Giyu and Sanemi denied the Ubuyashikis' gratitude and commended them for being the true reason the Corps remained until the end, Kiriya pushed aside his rigid and professional attitude and broke down in tears when Giyu remarked that his father and ancestors would be proud, along with his sisters. As seen in Tanjiro's update on events after the battle, Kiriya continues to keep tabs on the retired members, and he even sent Tanjiro and Nezuko a large sum of money to financially support them; when they rejected the money, he simply sent more.

Kiriya is a boy with light, pale skin and large, purple eyes. He initially had the same hairstyle as the rest of his siblings; a blunt bob with a fringe covering his eyebrows, colored black. As he was raised as a girl, he takes on a more feminine appearance during his first appearance, including having pronounced eyelashes and red lips. During Final Selection, Kiriya wore a purple uchikake kimono with patterned flowers and a green obi, supported with a white obiage and indigo obijime along with a white juban under everything. His head is adorned with a wisteria headpiece. After Kiriya becomes the leader of the Demon Slayer Corps, he stops dressing like a girl and removes any feminine features, such as his makeup and his wisteria headpiece. He instead wears a black kimono with a long white haori that is reminiscent of his father. He also parts the fringe on his hair, adopting a hair style akin to his ancestors. More than a hundred years after the disbandment of the Corps, Kiriya is still alive in the present day as the oldest living person in Japan. He wears the same clothing he wore after succeeding his father, although he is shown to have grown bald with only a few strands of hair, gained heavy wrinkles, and is very diminutive.

Extraordinary Memory: Kiriya has shown extremely good memory. He and his sisters are able to map out and memorize the nearly constantly changing Infinity Castle, creating accurate maps to navigate and guide the Hashira through it in real-time. Foresight: Similar to his father and his ancestors, Kiriya has a high, almost prophetic intuition, being able to make accurate guesses and hypotheses that were often proven right through intuition alone. Leadership Skills: Much like his father, Kiriya displays advanced skills in leading and commanding an army into battle despite his young age. He is able to immediately take command of the Demon Slayer Corps' command structure and assist the Hashira as logistical support, guiding them into battle. Longevity: Due to their relative, Muzan, becoming the first demon, men within the Ubuyashiki family were cursed with a mysterious illness, causing them to usually die in their thirties. However, after Muzan's death, the curse was seemingly lifted. In fact, Kiriya was blessed with an unusually long life, still being alive over a hundred years later and currently being the oldest living person in Japan.