Muzan's Blood Demon Art is called “Biokinesis”, which grants him the ability to manipulate his body at will and shapeshift instantly. Though all demons have this innate ability, Muzan takes it to another level by changing his flesh and organs.
Muzan has the ability to change his appearance and form.
After he neutralizes Tamayo's poison and emerges from his flesh cocoon, Muzan's hair grows in length and turns white due to Shinobu's poison accelerating his age. He also grows numerous mouths all over his limbs, each one lined with a set of incredibly sharp fangs.
Here Muzan is seen in his true, demonic form.
Before he can kill him however, the mansion explodes, with Muzan caught in it. 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.
The two known demons who broke free of Muzan's curse are Tamayo and Nezuko. Tamayo was able to break free of the condemnation when Yoriichi fought Muzan, nearly killing him in the process. During this weakened state, Yoriichi let Tamayo go, free her from Muzan, and free her from the curse.
2 His Body Is Weak To Certain Poisons
Poisons that did not exist before, like Tamayo's concoction of turning demons into humans, are the kind of poisons that Muzan's body isn't prepared for, as he's never been exposed to them before, and thus, his body has no idea as to how it should fight those poisons.
Based on the familiarity in which the two conversed at the end of the story, and the fact that she was beside him when he fought Yoriichi, suggest that he did have some fondness for Tamayo, though why in never covered.
Muzan's Blood Demon Art is known as “Biokinesis.” It allows him to alter his body and shapeshift at will. Although all demons have this innate ability, Muzan elevates it by modifying his flesh and organs. Biokinesis is also the only reason Muzan has been able to hide from the Demon Slayer Corps for 1000 years.
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.
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.
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.
The only reason why Muzan hates Doma is because of his insincerity and lack of emotions. This might sound odd, expecting emotions from a demon, but even a demon has to retain such tendencies to keep things in order.
It's true that in later episodes, Muzan also appears as a woman wearing a kimono when he's holding court over other Demons, most of whom are also wearing traditional Japanese clothing. This might have something to do with Demons (or “Oni”) themselves being part of traditional Japanese culture.
As of now, Muzan himself cannot walk in sunlight, and his ultimate goal is to walk in sunlight again and no longer be limited to the night.
Tsukito, Yorogi, Kuraku, and Isatsu all agree that they are loyal to Muzan.
Haruka Shiraishi: Muzan's Daughter.
Muzan's loyal wife and daughter seem like convenient test subjects to help him synthesize a cure for sunlight weakness as a backup in case the Blue Spider Lily is never found. The young girl might even be Muzan's biological child, a half-demon who gives off the scent of a human while having his essence in her.
It is revealed that Tamayo's drug had an aging potion mixed in along with the Demon antidote. Due to this, Muzan has aged 9,000 years within the span of three hours.
Does Muzan have a favorite demon? Despite the fact that Muzan. is always shown to have disdain for his creations, Muzan does in fact have a favorite. On that list is Naki, made due to a convenient blood demon.
1) Kokushibo
He is the only demon to have a breathing style in the Demon Slayer series. In fact, Muzan views him as more of a business partner and one of his closest allies. Thanks to this treatment, Kokushibo is extremely loyal to Kibutsuji and remains his strongest enforcer.
So, in conclusion, her coming from a Sun Breathing user's lineage and not relying on human substance are perhaps the reasons for her immunity. Hence, Muzan was searching for the Blue Spider Lilly, a flower that was a crucial ingredient in the medicine used by the doctor who saved his life.
As Nezuko can't speak Muzan's name out loud, she can't be affected by the curse.
Muzan can't control two powerful ladies
According to Comic Book Resources, since Nezuko is able to cling to the humanity she has left, she's also able to block out Muzan's influences. The second demon that Muzan can't control is the kind and smart Tamayo (Maaya Sakamoto and Laura Post).