Tanjirou and Giyuu are the first one to approach him. There they fight Muzan Together without stopping. They realized that the only way to kill Muzan is to drag him into the sun.
The Demon Slayers vs Muzan Kibutsuji Part 1 is a battle takes place in both the Demon Slayer Corps Headquarters and the Infinity Castle. It is the first major confrontation between Tanjiro Kamado, The Hashiras, and Tamayo against the Demon Lord Muzan Kibutsuji.
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.
Originally a human, Muzan suffered from a terminal illness, during an experimental treatment, Muzan became the first ever demon. He is also the progenitor of most other Demons and the leader of the Twelve Kizuki. He is also the archenemy of the Kamado family and both Tanjiro Kamado and Nezuko Kamado.
Yoriichi Tsugikuni, the first swordsmen to ever use Breathing Styles, once nearly killed Muzan with Sun-Breathing, and Muzan has been both physically and psychologically scarred ever since.
Yoriichi defeated Muzan in an instant, but he had a question for him before eliminating him, which allowed Muzan to escape.
Moreover, Tanjiro's appearance somewhat resembled Tsugikuni. So the only reason Muzan is afraid of Tanjiro is because of the Hanafuda earrings he possesses, which acted as a reminder of his downfall.
Curse of Kibutsuji
This curse besotted any who partake of Muzan's blood must be careful. The curse prevents Muzan's name from being spoken aloud, and any who do will meet a horrible demise.
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.
Haruka Shiraishi: Muzan's Daughter.
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 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.
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.
TikTok. Have you ever wondered how loyal is Akaza to Muzan? Since Akaza became a demon, he's been a loyal subordinate to Muzan for centuries.
Ainz's spells are so deadly that they can make Muzan's demon blood boil with fear. He's taken down some of the most powerful foes with ease, including Shalltear and Jaldabaoth, who are themselves stronger than Muzan Kibutsuji. Muzan may be the king of demons, but he's no match for Ainz's spell-slinging skills.
Yoriichi Tsugikuni was the first Demon Slayer and also the one who invented Breathing Techniques in the first place. Yoriichi was born with the Demon Slayer mark and prowess in swordsmanship. His powers were beyond comparison as he defeated Muzan once and had him on the verge of death until he managed to escape.
No they would not the fight happened, in the manga and the Hashira needed “extensive” outside help to beat Muzan Rengoku Muichiro and Tengen weren't there because two are dead, and one retired but the 9 Hashira by themselves cannot win.
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.
Enmu was one of the demons serving under Muzan, the first of his kind as well as the Demon King. They first met when Enmu was a human and Muzan consumed his guts.
Thus, Muzan created demons for hundreds of years even when he didn't want to turn someone. 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.
As Nezuko can't speak Muzan's name out loud, she can't be affected by the curse.
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.
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.
The black blade represents the Sun and is surrounded by prejudice and misconceptions, as historically every demon slayer who held it lived a short life. This could mean that Tanjirou is destined to break the pattern and set a new legend for black Nichirin blades in the Demon Slayer universe.