Nezuko doesn't stand a chance against the Upper Moon 3 She underwent a transformation and thoroughly overwhelmed the Upper Moon 6 demon. That being said, there is absolutely no way Nezuko can even come close to beating Akaza.
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.
In this state, referred to as her Berserker Form, she easily overpowered Daki, who holds the rank of Upper-Moon Six (a title she shares with her brother). Nezuko's raw power is undeniable as she bludgeoned Daki to pieces before burning her almost beyond repair with her Blood Demon Art, Pyrokinesis.
Sanemi's sheer power and speed will be able to overwhelm Nezuko even in her final form. Nezuko's Blood Demon Art would not work against Sanemi since he's a human, and he has the ability to decapitate her head if he wanted to.
Since Nezuko isn't a part of the Twelve Kizuki, she doesn't get a demon rank. She does however have her own demon blood art, as well super-fast reflexes and the ability to grow and shrink in size.
The only upper moon that Nezuko can defeat is Daki, it was shown that she was indeed stronger. However, she doesn't stand a chance against the other upper moons.
Nezuko can be ranked at the level of an Upper Moon 5 since she is considerably weaker than the likes of Kokushibo and Doma.
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.
While she might not be as powerful as Muzan himself, her overall strength makes her easily comparable to an Upper rank demon.
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.
1 Exploding Blood/Pyrokinesis Blood Demon Art
By far, this is Nezuko's most damaging technique when it comes to fighting her own kind.
So if Nezuko ate a human. and continued to do so over time, her power could rival that of Upper Moon one or 2, and here's why. One, if you're a manga reader, you know, in her base, Nezuko conquers the sun. And 2, her blood demon art can nullify.
Her most prominent traits is her extraordinary growth rate possibly due to the high amount of blood she received from Muzan Kibutsuji when he turned Nezuko into a demon and the fact that she doesn't need to consume human blood to survive.
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.
Weaknesses: Wisteria flowers are poisonous to her. Exposure to sunlight used to be lethal, but no longer affects her. Notable Attacks/Techniques: Blood Demon Art: Blood Burst: Nezuko ignites her blood and turns them into flames that only burn demons and their blood demon arts.
If Zenitsu fought Akaza with his plethora of Thunder Breathing techniques, the latter wouldn't have the time to regenerate his limbs.
Nezuko's Sunlight Immunity in Demon Slayer is Tied to the Blue Spider Lily. Nezuko having eaten the Blue Spider Lily at some point could explain her immunity to sunlight, and Demon Slayer: Kimetsu no Yaiba has already worked to justify that.
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.
After various battles within the Dimensional Infinity Fortress the remaining Upper Moons are killed by the hands of various Demon Slayers. 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.
Sanemi Shinazugawa
In their initial encounter, Sanemi held a deep hatred towards Nezuko due to her nature as a demon.
Mitsuri Kanroji is another Hashira who Tanjiro could definitely beat in Demon Slayer.
In his first appearance, the Wind Hashira Sanemi Shinazugawa discovered Nezuko Kamado and tried to agitate her by stabbing her repeatedly. When that didn't work, he cut his arm in an attempt to get her to bite him and prove she was no different than any other demon, ignoring Tanjiro's pleas for him to stop.
How Doma became the worst demon in Demon Slayer. Almost every creature possesses emotions, be it anguish, sorrow, happiness, or even fear. However, in the case of Doma, he doesn't feel a thing. During his childhood, his mother stabbed his father to death for cheating on her and, later on, took her own life.
However, against all odds, Tanjiro along with the rest of his crew were able to defeat the Upper Moon 6.