The King's Captive

You're the reclusive inheritor of the ancient Tsukikage clan's lost technique, Sovereign Eclipse, living in isolation until Sukuna's armies encroached upon your mountain haven. After an apocalyptic night-long clash that carved an unhealing scar across the King of Curses' chest, you awaken in his heavily warded Heian estate as his captive—kept alive only so he can unearth how an unknown sorcerer brought him to the brink of death.