Muzan is cold-hearted, ruthless, intimidating, and exceptionally intelligent. He sees no value in any humans he has encountered and shows little value in his own subordinates. Rarely ever visibly upset or happy, he appears completely monotone and detached on most occasions, even when he callously murders his own subordinates. The only times he ever shows emotion are when his vision of perfection is moving forward or when he has subordinates completely submit to his will. The manga shows him to be more expressive, particularly when enraged and his facial features are exaggerated to demonstrate as such. His inflated ego and delusional sense of self worth are so large, he cannot stand being mocked or corrected in any fashion, believing that others only exist to serve him. This also means he rarely ever takes any opponent or threat seriously. Muzan has unpleasant memories of his weaker, human past, and is very self-conscious of his unnaturally sickly appearance.

The most prominent trait Muzan possesses is extreme narcissism, pettiness, and an obsession with becoming the perfect being. As he has had over a thousand years to live and observe, along with hardly any real challenges, his extreme egocentrism is almost expected. He considers almost nothing to be his concern except overcoming his inability to walk in the sun, which is his primary drive. His long life and obsessions have caused him to want every plan he concocts to be absolutely perfect, and his superiority complex prevents him from seeing his own failures. His belief that he is the closest thing to a perfect being causes him to have zero tolerance for any failure, brutally punishing those who fail him or those he considers weak, even if the failures are minor. Behind the myriad of façades he displays, and completely offsetting his insatiable ego and lust for perfection, Muzan is unbelievably cowardly. He always seeks to avoid conflict whenever possible.

He has shown himself to be very manipulative and cunning, being able to blend in human society normally, even having a family of his own to add. A long life and continued practice has allowed him to take on many roles in society and play them capably, including children and women should he choose to. This life has also given him great intelligence and the ability to think tactically. Being a quick-thinker and strategist enables Muzan to be able to deal with unfavorable situations rapidly and successfully, though this may also be because the loss of his subordinates means nothing to him in the long run.

If you could sound similar to his English VA, Greg Chun, that would be great, but it is not required!

English VA Example: https://youtu.be/xm0AiKWPYuQ?si=jtKKbnnpPmfm04PY -spread throughout the clip