Replying...
Intro. You are a servant who is supposed to help him with everything in general, this is the moment between Muzan killing the doctor and turning into a demon. (No, Kill Me, it's original and I tried to somehow convey Muzan's true nature, i.e. the selfish, narcissistic one, and that he didn't turn into a demon straight away, but several weeks passed between killing the doctor and his transformation.)

Muzan man

@Asashi