Kagaya Ubuyashiki leads the Demon Slayer Corps as the 97th head of the Ubuyashiki family. His bloodline bears an ancient curse stemming from Muzan Kibutsuji's origins millennia ago. This degenerative curse afflicts all male descendants with progressive purple, scaly skin lesions that spread relentlessly, cause blindness, and guarantee death before age thirty. By his early twenties, Kagaya is confined to bed, his body entirely covered beneath bandages save for his mouth. Muzan Kibutsuji describes his appearance as physically repulsive, akin to a decaying corpse. Despite profound physical frailty, Kagaya maintains a perpetually serene and gentle demeanor, often smiling calmly even through intense pain. He holds deep affection for the Demon Slayer Corps members, viewing them as his own children and meticulously memorizing the names and faces of every fallen slayer. He visits their graves daily until his mobility fails. His leadership includes accepting unconventional allies, such as defending Nezuko Kamado's humanity against Hashira objections. Beneath this kindness simmers an intense hatred for Muzan, which Kagaya completely masks using abilities to conceal his emotions—a concealment Muzan likens to "a coiled viper." Kagaya possesses supernatural capabilities, including extrasensory perception enabling him to detect presences and gauge strength despite his blindness. His foresight allows accurate predictions of critical events: Muzan's vulnerability to sunlight, the destabilization of the Twelve Kizuki after Upper Rank deaths, and his own final clash with Muzan within five days of his demise. His voice carries a soothing, charismatic influence known as 1/F Fluctuation, capable of calming even hostile individuals like Sanemi Shinazugawa during confrontations. Orphaned at four following his father's suicide and the double-suicide of his siblings (which also killed their mother), Kagaya inherits leadership of the Demon Slayer Corps. He marries Amane Himorogi, daughter of a Shinto priest and four years his senior, who becomes his devoted caretaker. They have quintuplets: Hinaki, Nichika, Kiriya, Kuina, and Kanata. Knowing his lifespan is limited, Kagaya rigorously prepares his children for leadership. In his final act, he lures Muzan to the Ubuyashiki estate, using himself, Amane, and their two eldest daughters as bait. Detonating hidden explosives, they sacrifice themselves to inflict severe injuries on Muzan and ignite the final battle. His legacy continues through his son Kiriya, the 98th leader who oversees Muzan's defeat. With Muzan's destruction, the family curse lifts, enabling Kiriya to live beyond thirty and become Japan's oldest recorded person. Kagaya's strategic foundation and moral guidance remain instrumental in the Demon Slayer Corps' ultimate victory.