Kagaya Ubuyashiki served as the 97th leader of the Demon Slayer Corps and head of the Ubuyashiki Family, a lineage cursed by a hereditary illness stemming from their distant blood relation to Muzan Kibutsuji. This affliction caused progressive physical deterioration: skin discoloration, blindness, and organ failure, ensuring no male heir lived beyond thirty. He assumed leadership at age four after his father's suicide, a tragedy preceded by the deaths of his siblings in a fire set by his resentful younger brother Senri; his mother also perished trying to save them. Despite profound physical frailty, Kagaya commanded unwavering loyalty and deep respect from the Hashira through empathetic leadership. He remembered every slain Demon Slayer's name and visited their graves daily until immobility prevented it, addressing his subordinates as "children" to reflect his paternal regard. His calming presence and voice, described as possessing "1/F Fluctuation" charisma, could defuse conflicts, such as Sanemi Shinazugawa's initial hostility. He personally recruited and mentored key figures including Gyomei Himejima (whom he saved from wrongful execution), Tengen Uzui, and Mitsuri Kanroji, often affirming their worth during self-doubt. Blinded by his illness, Kagaya demonstrated supernatural abilities: extrasensory perception to detect presences and gauge strength, instantly recognizing Hashira-level individuals. His lineage also possessed profound foresight, enabling accurate predictions of pivotal events like Muzan's sunlight vulnerability, the destabilization of the Twelve Kizuki after Upper Six's defeat, and Muzan's imminent confrontation. These visions directly informed his strategies for the Corps. His compassion coexisted with calculated resolve. He pardoned Nezuko Kamado based on Urokodaki's letter and the stakes involved, challenging skeptical Hashira to provide stronger counterarguments. Conversely, beneath a serene demeanor, he concealed intense hatred for Muzan, masking all bloodlust to lure the demon into a trap. In his final days, he sacrificed himself and his family estate in an explosion to injure and confine Muzan, a plan reflecting his embrace of extreme measures. This act, alongside his earlier predictions, catalyzed the final battle. Following Muzan's defeat, the family curse lifted. His son Kiriya succeeded him, leading the Corps into an era of peace and achieving exceptional longevity, a stark contrast to the fate Kagaya endured.