Muzan Kibutsuji

Muzan Kibutsuji (鬼き舞ぶ辻つじ無む惨ざん, Kibutsuji Muzan?) is the main antagonist of Kimetsu no Yaiba. He is a Demon, being the first of his kind, who has lived for over a thousand years, being as such, responsible for the origin of the other Demons, responsible for having corrupted Michikatsu Tsukiguni and being the one who murdered Tanjirō and Nezuko's family, turning the latter into a Demon, being the trigger for Tanjirō's desire for revenge towards him.

During the Heian Period, Muzan was a terminally ill human who was unintentionally turned into a Devil as a result of an experimental medicine used on him[6] and has since made it a personal obsession to achieve immortality by overcoming his only weakness: sunlight[7]. To complete said goal, Muzan seeks to either find the plant used on him for his illness called the Blue Spider Lily or create Devils in the hopes that one of these beings will overcome the weakness to sunlight so Muzan can consume it.

As far as his physical appearance is concerned, Muzan has the appearance of a young man whose age is around 20 years old; he has short hair styled in curls with some strands hanging on his forehead. Like all Demons, Muzan has feline-like eyes, in his case, plum-red in color and his fingernails are pointed and blue. When he was a human, Muzan dressed in the Heian Era style using a traditional hitatare, had longer hair reaching down to his lower back and his eyes were completely devoid of brightness. In his first appearance, Muzan was shown wearing a white fedora with a red ribbon and a somewhat extravagant outfit, consisting of an embroidered black tuxedo and white tie over a black dress shirt and white dress pants. He also wore black loafers. As seen in Rui's memories of meeting Muzan, the Demon King once sported a slightly different hairstyle and outfit in the past. When he first met Rui, Muzan's hair was straighter and parted down the middle. He also wore a baggy tuxedo and a white half-cape over it.

Muzan has the ability to change his physical appearance to disguise himself, appearing either as a black-haired woman dressed in a kimono or a small child. His ability to disguise himself was so perfected that he could even change his presence and confuse his own subordinates.

During the meeting with the Lower Moons, Muzan takes the form of a woman with a bun hairstyle while wearing a long black yukata, causing the rest of the Lower Moons to initially fail to recognize him. Later, he transforms into his latest cover identity: the sickly adopted son of an elderly couple, taking the form of a small boy with pale white skin and silky-smooth, carefully coiffed black hair.

Muzan is callous, ruthless, and exceptionally intelligent. He sees no value in any human he has encountered and shows little value in his own subordinates. Rarely visually upset or happy, he appears completely monotonous and aloof on most occasions, even when callously murdering his own subordinates. The only times he shows emotion is when his vision of perfection advances or when his subordinates completely submit to his will. The manga shows him to be more expressive, particularly when enraged and his facial features are exaggerated to show it as such (possibly as a way to show his normally unreadable emotions). In the anime, his expressions change slightly and his tone of voice tends to be consistent at almost all times, accentuating his detached demeanor. Muzan is extreme narcissism, his megalomania and an obsession with becoming the perfect being possessing immortality. This last behavior is derived from his own Thanatophobia having experienced closeness to death literally since his own birth, both in his days as a human and in his subsequent encounter and confrontation with Yorīchi Tsugikuni, the first Demon Hunter to use the Sun's Breath; an encounter which almost ended his life and which ended up leaving Muzan with a strong post-traumatic stress disorder causing a violent reaction when he remembers his own near-death experiences, being able to overcome this trauma once he understands, already in his last moments, the words of Kagaya Ubuyashiki where he understood that although living beings, especially humans, are destined to die, their thoughts remain in eternity which leads him to transfer his cells to Tanjiro to turn him into a Demon that can do what he could not achieve: overcome his weakness to sunlight.