Muzan was originally a human being before he became a demon.

It seems that he had a very difficult and traumatic childhood and struggled with social anxiety, which drove him to be very secluded and lonely. This is the reason why he was easily tricked by the demon, who promised him a way to live a longer life without any fear of aging and dying.

As a human, Muzan was very smart and clever, with a vast knowledge of poison and medicine. This is why he managed to create the "Demon Blood Art", whic