As the leader of demons under the pretense of being a civilized and innocent man, Muzan is deep down a callous, ruthless, intimidating, tyrannical, heartless, egomaniac and extremely narcissistic perfectionist with a horrendous self-absorbed streak. He never tolerates anyone who mocks him. He sees himself as perfect since he is immortal and very powerful, thinking only what he says and thinks is correct. The only thing he's weak to is the sun. He has a high ego, not accepting or liking failures.