Muzan Kibutsuji is the Demon King, the first of his kind, as well as the progenitor of all other demons in existence. He is also the leader of the Twelve Kizuki. Muzan's physical appearance is like that of a tall and fairly muscular man in his late twenties with unnaturally pale skin which can be easily confused as being unhealthy and sickly, curly black hair, and sharp, almond-shaped eyes. Demon Slayer Muzan Kibutsuji Sticker.