「What I adore is invariability, something that stays perfect and never changes.」
CV:Toshihiko Seki（the same as other forms）
Muzan is a human devouring demon, the first of his kind, who has lived for more than one thousand years. He is also the demon responsible for slaughtering the family of the protagonist Tanjiro and turning Nezuko into a demon.
His blood can turn a human into a demon and enhance a demon’s strength. And he is the only one who can do this.
Muzan does not trust any of his subordinates. He possesses the ability to put a curse onto all the demons he creates by sharing his blood. If any demon he creates even utters or says his name out loud the curse will activate and destroy them.
His appearance changes from time to time, sometimes he is a modern gentleman 「Kitsuhito」, sometimes he is a smart boy 「Toshikuni」and sometimes he is a flamboyant lady. Moreover, no matter which appearance he adopts, people would act like『he／she has been existing in their lives for a long time』. He might brainwash people around him every time he changes his appearance, or he is just able to replicate himself. The details are unknown.
When he walks in the street in human disguise, he usually is accompanied by humans who seem to be his family or lovers. Sometimes, he would transform into the adopted son in a rich family.
As it is mentioned above, he changes his appearance from time to time. This contradicts his statement of hating changes and adoring invariability. Maybe as a demon, there is always a twisted side of him.
Basically, he curses his subordinates-the demons and treats them ruthlessly. He would unconcernedly kill members of Twelve Demon Moons who serve him as demon cadres not because they have made a mistake, just because he wants to.
He ruthlessly killed four Lower Moon members no matter how earnestly they begged. He left one for last because Enmu’s statement satisfied him, so he gave Enmu 「an ample share of his blood. However, if Enmu was（ not able to withstand the volume of the blood she would die」. It was actually more a death sentence than a life chance. He is just a dyed-in-the-wool cold-blooded creature.
On the other hand, he likes the most inhuman and outrageous demons. He would approach these demons; even inject them with a large amount of blood as a kind of preferential treatment.
Besides, he seems to like demons that have bigambition, though he never shows it.
There seems to be a connection between him and the hanafuda earrings Tanjiro wears.
Muzan is a cold-hearted ruthless and arrogant monster. He is extremely cruel and never shows any mercy not only to humans but also to demons.
Tanjiro has met many demons. Demons were humans. Some become fanatical under Muzan’s manipulation. Some are in pains and regrets of being demons. To Tanjiro, all of them are just 「vain and pathetic creatures」. Muzan is different. In Tanjiro’s words, he is 「the true demon」.
Besides, Muzan does not understand the Demon Slayer Corps who have been sacrificing their lives trying to seek revenge for their beloved ones. To Muzan, the Demon Slayer Corps are an assembly of aberrations.
He believes that he is the 「closest thing to a perfect being」. A human can be turned into a demon when injected a certain amount of his blood. However, if a human takes too much blood from Muzan, their cells would mutate faster than they can stand, causing them to self-destruct into one giant mesh of flesh.
As he claimed to be the perfect being, he possesses the unparalleled power. However, Muzan seems to be strangely vigilant to『something』. He hates to show his power and true appearance in front of the Demon Slayer Corps, and mostly hides himself in the crowd in human disguise.
Therefore, Muzan never fights the Demon Slayer Corps in person. Instead, he creates and spreads human devouring demons and has chosen a special group of demons- 『the Twelve Demon Moons』to serve under him and fight for him.
He puts a curse onto demons to secure their absolute obedience. And only in front of them (the demons) he would show up. Tamayo thinks that Muzan is a 「coward」. And this strange behavior pattern to some extent indicts his cowardice.
Once, a drunk man bumped into Muzan. Instead of killing the man immediately, with a strange calmness he restrained himself at first and killed the drunk man only after being mocked to have 「a pale face」, which in turn accentuated his eeriness.
the supercilious dictatorial black boss
As it is mentioned in the overview part, Muzan is totally ruthless to his subordinates. He shows up only for sanction and reprimand. He would assemble the cadres and vent his anger on them every time something happens. These scenes are mocked by the readers to be the black meeting.
Muzan looks like a calm and composed person. However, if someone notes how pale he is, he would overreact and kill the person. He would easily get irritated by the subordinates’ mistakes. To some extent, Muzan has an emotionally unstable and childish side.
For such a disposition, Muzan would do something that would undermine himself, such as making unnecessary enemies, suffering an unexpected blow, destroying a perfect cover just on a whim. However, he doesn’t care at all and insists that 「I’ve done nothing wrong」.
The manga fans call Muzan the man who slays most of the Twelve Demon Moons for he has killed four members of the Twelve Demon Moons, one demon more than Tanjiro who, as a demon slayer, has killed three members of the Twelve Demon Moons, which is also a record inside the Demon Slayer Corps.
As a living“creature”, Muzan is superior to other creatures in every possible aspect.
He is immensely superior to demons which are overwhelmingly strong compared to humans. He is the only one who can turn a human into a demon. To be precise, he is a different (superior) kind of creature from demons. Therefore, a Nichirin Sword decapitation cannot cause his death 。
For Muzan, being“the strongest”is just a temporary phase to pass. He is infinitely close to “omnipotence, thus to beinvincible”. As omnipotent as Muzan, he would easily eradicate the Demon Slayer Corps. However, he deliberately stays away from the frontline.
The sheer swinging speed of his attacks is extremely fast. He has killed the Lower Moon Three who was fleeing at his highest speed and Upper Moon Five who just slipped out some careless words in an instant before other demons even noticed. He also has killed instantly all the demon slayers who were encircling him. His speed is way beyond extraordinary.
Furthermore, Muzan can use his own blood to create several spiked-barbed wires to entangle his enemies. This technique is called 『Spine of Thorns』and was once applied to Gyomei Himejima, but no real damage was thus formed. This technique might just be a small trick of Muzan. Besides, there is no further information about this technique.
※the following content may contain spoilers
「Finally, there comes the one who can conquer the sunlight ……！！ Hantengu, good job！！」
「There is no need to searching for the Blue Spider Lily anymore. It has been too long…！！」
「Only for this, only for this, I have been creating congeners that I never want for a thousand years.」
「 Even the Twelve Demon Moons never has the sign. She is the chosen demon」
「If I absorb that girl, then I can overcome the sun！！」
In chapter 127 (15th volume of tankobon), there is a brief introduction about how Muzan turned into a demon.
He was originally a man born and living in Heian Era. It seems that Muzan was an aristocrat and there were scenes about his life in a mansion.
He was congenitally feeble and diagnosed by a doctor(kusushi) that 「he would die before he turns twenty」. The kind doctor had worked hard to try to find a way to let him live a little bit longer.
In order to cure Muzan, the doctor gave him a special prototype medicine. In a burning rage, resulting from his worsening condition, Muzan killed the doctor by throwing a knife into his head from behind.
Ironically, shortly after the doctor’s death, the medicine started to work. Muzan got better and even acquired a strong body no human can be compared with. On the other hand, he became vulnerable to sunlight and desiring for human flesh. It was the moment he became “the first human devouring demon”. Muzan had no problems adjusting to having to devour humans for survival, but the problem he faced was the fact that he was unable to walk in the sun. The sun was fatal to him, forcing him to resort to doing his activities only during the night, a condition that he resented. So he started to look into the formulation of the medicine 『Blue Spider Lily』the doctor used for his treatment. He found out that Spider Lily was used and started his journey across Japan searching for Spider Lily for more than a thousand years. Let alone its habitat and cultivation, he even had not figured out yet whether the Blue Spider Lily was literally a kind of blue-colored Spider Lily or just a metaphor.
In order to overcome the sunlight, 『finding the Blue Spider Lily』 and creating and spreading more demons in hope of an evolving demon that can overcome sunlight become Muzan’s top priorities.
Thus, Muzan did not like the demons he created. However, when informed by Hantengu about 「a clue to the method of overcoming sunlight」, he instead of scolding, appraised his subordinate for the first time. And it was also the first time he admitted outright that demons were 「congeners he never wanted to create」. In a word, he treated all of his subordinates including the Twelve Demon Moons ruthlessly because he just hated every demon except himself.
⚠️Spoiler alert（not mentioned in tankobon volumes）
「You are all useless. I will destroy the demon hunting games tonight. I will kill them all.」
After suffering from the explosion of Ubuyashiki estate, Tamayo’s drug and Himejima’s all-out attack trying to destroy his head and attacks from the Demon Slayer Corps in the Dimensional Infinity Fortress, Muzan shapeshifts to a cocoon of flesh in order to recover. And in chapter 180, Muzan emerges from his flesh cocoon to the combat form. His hair turns a pale color. He also grows a large amount of mouths all over his limbs. His skin also appears to have a dark-red mass growing onto most of his body. And finally he declares that he will annihilate the Demon Slayer Corps with his own hands.
- Kars（JoJo's Bizarre Adventure）… also wants to become the 『perfect being』. And his goal is to become eternal and immune to the sun’s rays.
- Naraku(Inuyasha)…Like Muzan, Naraku is also「searching for the way to become stronger, and he is also a giant monster of vile character」. Moreover, Naraku also lives in the old time Japan (different period from Kimetsu no Yaiba).
- Aleister Crowley… Similarly, the character resides in a base(Aleister has the 「Windowless Building」 and Muzan has the Dimensional Infinity Fortress ) where access to the place is only by guiding by a certain person （Awaki Musujime is the guide to the Windowless Building, and Nakime is the guide to the Dimensional Infinity Fortress）. Both are the last boss(Aleister loses his position to another person, so he decides to assist the protagonist). Both can shapeshift to female forms (Aleister disguises as a beautiful young girl, and Muzan disguises as a flamboyant woman). Not limited to the above, there are also many other similarities. However, unlike Muzan who would some stupid things and still insist that 「he hasn’t done nothing wrong」, Aleister would postulate a failure of his every movement. He believes that one has to overcome the failures and moves towards the goals. It can be said that Aleister’s understanding of 「failure」is opposite to that of Muzan.
- Voldemort…Similarly Voldemort is extremely cold and does not trust anyone including those are very close to him. He also is obsessed with becoming eternal. Even though, Voldemort trust his partner snake Nagini. And he does not recklessly kill his subordinates（he even forgives Lucius Malfoy, and allows him to join his newly-assembled army.）
Moreover, he only manipulates souls and does not try to surpass human beings.
- Iruka Umino… Like Muzan, this Iruka Umino is also a Jump manga character and a key figure deeply involved in the principal of action of the protagonist. However, in terms of stance and personality he is the antithesis of Muzan.