Partnering with Kokushibo, Upper-Rank One of the Twelve Kizuki and the brother of Yoriichi, Muzan and his most powerful demon traveled around Japan, killing anyone who'd even heard of Sun-Breathing.
Hoshiko Kibutsuji. The first female demon [of a different orgin], and the younger sister to Muzan Kibutsuji. She loves her brother and was the one who had attacked that man who wore the hanafuda earrings.
It was then revealed that Muzan and Kagaya are from the same family which led to the Ubuyashiki family being cursed where every child born will be weak and die right away.
Ubuyashiki Family
He is a distant relative of Muzan and his entire bloodline was cursed with a disease that slowly kills them before reaching their thirties, possibly because of their connection with Muzan's blood.
It is later revealed that Muzan is of the same bloodline as the Ubuyashiki Family.
Yet an official Demon Slayer "fanbook," written by the manga's creator, Koyoharu Gotouge, revealed Muzan doesn't really like Upper Rank Two demon, Doma. As Lower Ranks Six, Four, Three and Two can attest, Muzan is not averse to eliminating demons he doesn't care for, even if they're Kizuki.
Muzan is shown to have a positive master-servant relationship with Daki, as the young Demoness seemingly worships and admires the Demon Progenitor immensely, fervently hanging on each and every one one of his words and doing her absolute best to accomplish the tasks he gives her.
Akaza was also one of Muzan's favorite demons out of all his subordinates. The reason behind this is Akaza's extreme loyalty to his master.
Muzan Kibutsuji (鬼舞辻無慘, Kibutsuji Muzan) is the main antagonist of the Demon Slayer: Kimetsu no Yaiba fantasy action manga and anime series. Muzan is the powerful King of all the Demons, who has the ability to inject his victims with blood that allows him to convert them into more Demons.
Haruka Shiraishi: Muzan's Daughter.
The warrior Muzan feared was a swordsman named Yoriichi Tsugikuni. Yoriichi was the only slayer before Tanjiro who came close to killing Muzan, and the flashback of their fight occurred in Chapter 187.
Since he didn't know anything about the Blue Spider Lily medicine, he needed others to find the plant for him by happenstance. This is the general reason why Muzan turned Nezuko into a demon. More specifically though, was the fact that Nezuko was of Kamado blood.
Muzan can detect the locations of his demons and can also read their thoughts. However, Nezuko and Tamayo are the only exceptions in the entirety of Demon Slayer, over whom Muzan has no control.
Yoriichi was powerful enough to defeat Muzan; however, he couldn't do so. That's because he couldn't come down to kill his twin brother, leading to his own demise. Even to this day, Muzan is scared of Yoriichi.
Muzan has had more than one family over the course of his millenia-long life. This includes the birth family he had before he became a demon. In addition to them, Muzan took five wives.
Sunlight: Muzan is noted to be immune to being killed via decapitation, as seen when Gyōmei destroyed his head and he still managed to regrow it. Thus the only other known way that he can be destroyed is by sunlight.
Abilities. Demon Body: Unique from other demons, he possesses seven hearts, and five brains. These are responsible for his powerful vitality, should any of them be harmed, he will be severely weakened.
For those who have watched only the first season of the anime, they will be surprised to know that Muzan turns into a woman in the second season. He keeps transforming in order to hide his true identity, and he's even known to change into an 11-year-old child to hide from Demon slayers.
Tsukito, Yorogi, Kuraku, and Isatsu all agree that they are loyal to Muzan. and show the utmost respect to him.
The Anti-Kibutsuji Drug is a special four-stage drug that was created by the combined efforts and medical expertise of Tamayo, Yushiro and Shinobu Kocho with the main purpose of annihilating, Muzan Kibutsuji.
Anne was originally planned to be Muzan`s older sister, who died by the hand of a Demon Slayer but that idea was scrapped, as the author knew practically nothing about Muzan`s early life. Instead, Anne became his wife, by which he had two children.
Over his long lifetime, Muzan had a number of families. This includes the one he was born into before becoming a demon. Additionally, he took 5 wives, making each one's life miserable.
Nezuko, on the other hand, never was under Muzan's curse, it would seem. Instead, she used her will to protect her brother and other humans to fight off the curse. This is probably why Nezuko sleeps instead of eating humans. This also means her strength as a demon is based on her will to protect rather than feed.
He was soon decapitated by the combined force of Kanao and Inosuke, avenging Shinobu and her family. Trying to struggle for survival like Akaza, but lacking indomitable willpower as Akaza had, Doma's head slowly disintegrated and he met Shinobu's soul in the limbo, holding his severed head.