Kagaya Ubuyashiki led the Demon Slayer Corps as its 97th head and patriarch of the cursed Ubuyashiki bloodline, bearing an inherited illness from their ancient tie to Muzan Kibutsuji. This affliction ravaged his body with progressive decay, blindness, and agonizing pain that confined him, shriveling his skin and requiring full bandages. Males in his lineage rarely survived past thirty. He inherited leadership at age four after his father’s suicide over Corps losses. Tragedy deepened when his eight-year-old brother Senri, resentful of the curse, ignited their home in a murder-suicide pact with six-year-old Akito; their mother perished saving them, leaving Kagaya sole heir. At thirteen, he wed Amane in an arranged union she embraced willingly, fathering five daughters—Hinaki, Nichika, Kanata, Kuina, and Kiriya—and one son. Despite his frail form, Kagaya inspired fierce devotion across the Corps, treating every slayer as his child. He memorized each fallen warrior’s name and face, visiting graves daily until immobilized. His leadership balanced compassion with strategic clarity: he resolved Hashira disputes, championed unity, and overruled their objections to shield Nezuko Kamado after discerning her harmlessness. He staked his life, Giyu Tomioka’s, and a ritual suicide vow on Nezuko’s restraint. His unnaturally tranquil voice, carrying "1/F Fluctuation," pacified even volatile spirits. Blindness hid neither presences nor power—Kagaya’s extrasensory perception identified Hashira at gatherings and sensed Muzan’s approach miles away. Foresight revealed Muzan’s sunlight weakness, the Twelve Kizuki’s collapse after Upper Six fell, and his own death within five days. Behind his serenity festered hatred for Muzan. In his final hours, he masked this venom behind a beatific smile, luring Muzan to his estate. There, Kagaya triggered hidden explosives, sacrificing himself, Amane, and daughters Hinaki and Nichika to cripple the demon king. Only in the blast’s aftermath did Muzan recognize Kagaya’s "coiled viper" wrath. Kagaya perished in the explosion, but his gambit enabled Muzan’s defeat. The curse shattered with Muzan’s death, freeing his son Kiriya—the Corps’ 98th leader—to live as Japan’s oldest recorded human. Kagaya’s legacy endured through the demons’ fall and his family’s reclaimed future.