1 Muzan (Demon Slayer) Without that antidote, it would have been impossible to kill him. So despite all her strength and humanity, Nezuko would have easily lost to Muzan.
Muzan, the King of Demons, is the strongest and also the primal demon in the world of Demon Slayer. Consuming his blood is enough to turn you into a powerful demon. He can control all the demons in existence, with only people with strong willpower like Nezuko being an exception.
Muzan can only not control two demons that are Nezuko and Tamayo. Nezuko is able to cling to all the humanity she has left and she can also block his influence on her. Her strong desire of protecting her brother and the devotion towards her family makes her hard to control for Muzan.
Nezuko's Unique Blood Demon Art and Potential to Defeat Muzan Kibutsuj, the Demon Lord. The Demon Slayer's demons evolve and gain power by consuming human blood, eventually developing their own unique Blood Demon Art.
The demon slayers successfully defeated Muzan.
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.
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.
Nezuko's Strength
Despite being a demon, Nezuko has found several ways to circumvent the negative consequences of her condition. Her strong willpower is easily her greatest trait, as with it she was able to resist the urge to feed on blood and instead regains her strength through extended sleep.
In conclusion, Nezuko cannot beat Akaza in Demon Slayer. In terms of power, physical abilities, regeneration rate and overall combat ability, Akaza is far superior compared to Nezuko.
The Wind Hashira is one of the strongest Hashiras in the Demon Slayer series. He played a significant role in defeating Kokushibo and was able to inflict damage on Muzan. Sanemi's sheer power and speed will be able to overwhelm Nezuko even in her final form.
With this in mind, if Nezuko had also been murdered by Muzan, Tanjiro would have no reason to be empathetic toward demons. Her transformation gave him a perspective of both demons and humans, but without Nezuko becoming a demon he would have no reason to take their feelings into account.
This also explains why Muzan is after her, he wants to devour her in order to gain the ability to walk in the daylight. Muzan has been looking for centuries of a demon that can conquer the sunlight. After Muzan discovers Nezuko's ability, he decides to change his plans and pursue her for himself.
Secondly, Muzan would probably… eat Nezuko and Tanjiro in the hopes of obtaining their sun-resistance abilities, and also since he wouldn't be able to convince them to become demons to work under him. This would allow him to become the ultimate demon.
Nezuko's rankings in the popularity polls are as follows: Nezuko ranked 3rd place in the first popularity poll with 3,319 votes. Nezuko ranked 11th place in the second popularity poll with 5,000 votes.
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.
Although Gyutaro might be far stronger, Nezuko would only have to keep up against the demon until sunrise. Her Blood Demon Art is such that it only affects demons, which means there is a very good possibility for her to beat the Upper Moon 6 demons.
As the main threat occupying the position of Upper Moon Six, Gyutaro's Blood Demon Art is tremendously powerful and extremely dangerous. With it, he can perform various attacks using blood from different parts of his body, and project them from his sickles as well.
Zenitsu is clearly on the same level as Hashira. If we compare him to Shinobu, his speed is far better, while she lacks quite a lot in raw power. There is a good chance that he could beat Shinobu if the two decide to fight.
1 Exploding Blood/Pyrokinesis Blood Demon Art
By far, this is Nezuko's most damaging technique when it comes to fighting her own kind.
However, she wasn't immune to the sunlight initially, as she got burned badly at first. 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.
Giyu is one of the legendary Hashira, and he's brought down demons far more powerful than Nezuko. With his level of skill and impressive agility, he'd easily defeat Tanjiro's little sister. In fact, when Giyu first meets Tanjiro and Nezuko, he almost does kill the latter.
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 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 Muzan favored Gyutaro so much, he chose to incorporate the latter's sister Daki as well. The demon king believed that she was the only tool that could be used to control Gyutaro.