Webone of muzan's unnamed blood demon arts creates a large and long mass of grotesque flesh from his arm that comes with a giant mouth at the tip.
In his final struggle for survival, muzan is able to transfer the remainder of his blood along with his memories into a suitable body, turning his new.
Webdespite his fearsome reputation among slayers and demons alike, muzan had an illness that almost took his life in demon slayer, resulting in his intense fear of.