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.
Although Muzan would attempt a final push for survival by turning the Demon Slayer Tanjiro Kamado into a demon, this ultimately failed. With Muzan's defeat, all demons created through his blood have died, leaving Yushiro and Chachamaru as the only demons to have survived.
Sanemi managed to survive the battle against Muzan, if just barely. Unconscious and straddling the edge of death, Sanemi chose not to go to Heaven with his siblings, but to lovingly join his mother in Hell because she'd killed most of her children after she became a demon.
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.
Muzan may be strong, but he would be no match for a powerhouse like Cheng Hua, who earned the reputation of being the deadliest of the Devastation class demons in Heaven's Official Blessings.
Muzan may be strong, but Madara is on a whole other level. Madara has Sharingan, Rinnegan, and wood-style jutsu, while Muzan just has some fancy demon powers. He could easily read Muzan's moves with Sharingan, then use wood-style jutsu to pin him down.
The only thing he's weak to is the sun. That is why he turned other humans into demons and spread his blood so that one of them might find a solution against the sunlight, so he can become truly perfect.
It is revealed that Muzan's true fear of dying and immense desire to live and survive was due to him being born "dead," where his heart would constantly stop in his mother's womb and was assumed stillborn until he fought to breathe before his cremation.
The only Demon he despises the most is the Upper Rank Two: Doma. It is quite a shocker that the second most potent Demon in the Demon Slayer is not Muzan's favorite.
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. The Upper Rank Three demon was always sent away on special missions, something the Upper Rank 1 and 2 were often denied of.
The demon slayers successfully defeated Muzan.
Some of the characters who have faced Yoriichi and survived
This happened due to a treatment that had gone wrong. While he was being treated, Muzan killed the doctor because he was not able to observe any results.
Unable to fight back, Doma realized he was tricked but it was too late. He was soon decapitated by the combined force of Kanao and Inosuke, avenging Shinobu and her family.
The last member, Upper Moon Four Nakime, ends up being killed by Muzan Kibutsuji himself to stop the Dimensional Infinity Fortress from being controlled by his enemies.
Kokushibo was the final Upper-Rank to die during Demon Slayer's "Infinity Castle" arc. Muichiro, Genya, Sanemi Shinazugawa and Gyomei Himejima fought together against Kokushibo, though Muichiro and Genya were no match for him and were killed.
Tanjiro Kamado
Tanjiro is considered to be Muzan's main nemesis throughout the series.
Muzan himself never thought highly of Daki and didn't reciprocate her devotion whatsoever, only ever talking to her to sweetly manipulate her into defeating Demon Slayers on his behalf.
Akaza. Because of his desire to become stronger and Doma's strength allowing him to surpass himself to become Upper Two, Akaza harboured an intense hatred of Doma.
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.
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.
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.
14) Muzan Kibutsuji (over 1000)
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.
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.
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.