Technically, the elder of the two Sakuras` was actually Muzan`s child, by way of his mistress (Lady Jade Wong), who had one of her eggs inserted into Anne`s body.
Not only that, he's married a woman and has a child with her. The most logical conclusions would be to either blend in society as a human, or to use the woman because of her social standing. In either situation, Muzan puts his needs first and does not care what happens to his wife and daughter.
Is Muzan's daughter his biological daughter? Hisana Kibutsuji is the biological daughter of Muzan Kibutsuji and is half human, half demon. Prior to the events of demon slayer, Muzan marries a woman named Amaya Ubu... The Great Demon War ended 8 years ago.
During his final struggle, and as a way to slow down the effects of the sun, Muzan adopts an enlarged demonic baby form, approximately as tall as a 3 story building when standing up. In this form he has very pronounced blood vessels across his body, small claws in his hands and fanged teeth in his mouth.
It's true. 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.
Curse of Kibutsuji
The curse prevents Muzan's name from being spoken aloud, and any who do will meet a horrible demise. One demon, Susamaru, faced this reality when battling Tamayo. Susamaru accidentally shot Muzan's name aloud, attempting to defend his honor with her mind clouded.
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.
This allowed him to hide from the Demon Slayer Corps while he carried out his experiments in an attempt to create a demon without any weaknesses. Therefore it is quite evident that Muzan doesn't love his family. They are merely tools to achieve his goal of true immortality and wreak havoc in the years to come.
Yoriichi was incredibly proficient in his Sun Breathing, being able to take down demons effortlessly and even overwhelm the Demon King and strongest Upper Rank.
Among his myriad of dread-inspiring techniques in Demon Slayer, Kibutsuji Muzan has the ability to place a curse on any demon imbued with his blood. Should any demon he's created say "Kibutsuji" aloud, the curse is activated -- instantly killing them.
Anne was a kind and loving soul and was described as the only person that Muzan had truly loved, besides his three daughters.
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.
Tanjiro. Muzan speaks his last thoughts and turns Tanjiro into the new demon king and subsequently his spiritual successor.
Fun fact: The reason why Enmu was able to say Muzan's name out loud without dying is because they're married!
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.
Even 400 years later, Muzan's fear of Yoriichi remained fully intact, as simply laying eyes on Tanjiro's hanafuda earrings caused him to recall their clash.
The explosion, which was enhanced by spike traps, manages to injure Muzan. Before he is able to regenerate fully, Tamayo appears and uses her Blood Demon Art to keep him in place, while using a drug that can turn him into human. Using this opportunity, Gyomei Himejima appears and destroys Muzan's head.
The first demon that is said to have existed was Muzan Kibutsuji. The one who turned him into a demon was a generous doctor from the Heian Period, who wanted to save Muzan from death since, at the time, he was diagnosed with a disease which would kill him before he turned twenty.
Muzan injects Tanjiro with all of his blood, turning him into a demon.
Being a demon, Muzan is capable of living for many, many years. However, unlike other demons that have aged over hundreds of years. Muzan is well over 1000 years old. Despite achieving an age that no one else has, his appearance makes him look like an adult man in his early to mid-30s.
Muzan's ultimate goal is to attain an immortal body. He wanted to be able to walk in the sunlight and live forever. In order to gain this, he needed two things: the Blue Spider Lily and the body of a demon who could withstand the sun.
He has a wife and a daughter that loves him, but he is in the marriage for the sake of surviving. Muzan calls his wife, Tsukahiro. Those are the facts about Muzan Kibutsuji, the strongest and immortal demon from Kimetsu no Yaiba.
Over a century ago, Doma held the position of Upper Rank Six ( 上 じょう 弦 げん の 陸 ろく , Jōgen no Roku?), and during that tenure, he turned Gyutaro and Daki into demons and introduced them into the Twelve Kizuki.
As revealed by Kagaya Ubuyashiki, the Ubuyashiki family themselves are in fact related to Muzan by blood, with them being the descendants of his relatives from a thousand years ago.