When the sky begins to lighten, panic overtakes Muzan. Abandoning his offensive tentacles, he shifts his physiology into survival mode. He expands his biomass into a grotesque, colossal infant-like shell, commonly referred to by readers as his giant baby form. This grotesque wall of outer flesh acts as a physical shield, designed to absorb the oncoming ultraviolet radiation while his true core burrows beneath the earth to escape.
What follows is an extraordinary display of collective resolve. The Demon Slayer Corps throws everything at the monstrous mass. Unranked slayers drive supply wagons, city buses, and heavy debris into Muzan's path to prevent him from crawling into shadows. Gyomei anchors a thick chain around the monstrosity's neck, digging his heels into the cobblestones with every ounce of strength left in his failing body.
Tanjiro, pinned inside the outer layer of Muzan's flesh, thrusts his Nichirin blade outward, turning it crimson to scorch the demon internally. As the morning sun clears the horizon, the UV light strikes Muzan's exposed bulk. The immense heat ignites his cells. Screaming in silent agony, his massive shell blisters, turns to ash, and collapses into dust. Muzan Kibutsuji dies not from a severed neck, but because the sun burns away every single cell he spent ten centuries preserving.
