Question: is muzan the first demon?
Answer: Muzan Kibutsuji ( 鬼 き 舞 ぶ 辻 つじ 無 む 惨 ざん , Kibutsuji Muzan?) is a Demon, the first of his kind, the progenitor of many other Demons, and the main antagonist of Kimetsu no Yaiba.