Muzan's menacing and cold-blooded disposition. Muzan is cold-hearted, ruthless, intimidating, and exceptionally intelligent. Muzan is very cunning. He is perceptive enough to be able to seamlessly blend into human society and he even started a family. He is the demon king and will ask anyone to be a demon.. Muzan's physical appearance is of a young man with curly black hair and bright ruby red eyes, he looks like he’s in his late twenties.