Even if all the Lower Moons worked together they couldn't defeat a Hashira. Let's take a look at the weakest Hashira aka best girl Shinobu. Shinobu is so fast that the Lower Moons literally can't touch her. Her posion is also strong enough to kill any of the Lower Moons.
Indeed, none of the Hashiras are competent of vanquishing Upper Moons 3, 2, and 1 in a one-on-one fight. This is purely because there is no way they could subdue a demon who is able to reconstruct his head even after getting decapitated by a Nichirin blade.
Muichiro can defeat Akaza easily with his petite body that leverages his speed. Moreover, his ability of Transparent World can aid him in landing a fatal blow on Akaza's weak spot.
Gyomei is currently the strongest Hashira.
Even a mid-level Hashira can beheaded them while the lower moon are literally helpless and unaware of what has happened. In the case of the Upper moon, meeting the enemy means nothing but death.
5 Speed: Tengen
Rengoku's fight in the Mugen Train arc showed his incredible speed and reflexes. He was able to match Akaza's speed, and his movements were so fast that it was almost impossible for the naked eye to keep up.
After awakening his demon slayer mark, Giyu greatly overpowers Akaza. However, he is able to keep up with the fight only because of Tanjiro. If Giyu had soloed against Akaza, he would have died.
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.
Sanemi and Doma may be comparable in terms of power, but if they had to fight, Doma would probably emerge victorious. The reason Doma lost was because of Shinobu's poison that significantly weakened him. This eventually helped Inosuke and Kanao to defeat him.
Rengoku fought Akaza in the Mugen Train arc of Demon Slayer. The Flame Hashira gave his all trying to protect the ones around him, and he succeeded. He almost succeeded in decapitating Akaza's head by using his Esoteric Art.
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.
2) Kibutsuji Muzan
It required the combined efforts of multiple Hashiras and other members such as Tanjiro, Zenitsu, Inosuke and Kanao to defeat Muzan in the end. Despite his monstrous strength, he was no match for Yoriichi Tsukiguni.
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.
8 Shinobu Kocho, The Insect Hashira
That being said, she's arguably the weakest Hashira when it comes to pure strength. However, brawn is not the only way to determine power in Demon Slayer.
Kokushibo is the one who is potent enough to stand next in line as the strongest demon after the Demon King himself. For a demon who has been alive for more than 400 years, he has the capability to go head-on against more than one Hashira at a time.
He, along with Sanemi Shinazugawa were able to beat the Upper Moon 1, Kokushibo. The demon was in awe of Gyomei's physique and declared him to be the strongest Demon Slayer he had faced in 300 years. Gyomei also managed to use Transparent World which is something only a select few can do.
While Sanemi and Giyu are pretty evenly matched, it's possible Sanemi would win a fight between them based on his ruthless nature alone. Giyu has shown mercy, but Sanemi isn't the type to hold back for any reason.
Gyomei cannot beat Doma on his own..and thats because of Doma's ridiculous abilities..
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.
In a nutshell, Muzan, being the progenitor of demons, is not scared of Doma. However, he is irritated by his inability to decipher Doma's thoughts and feelings, which is the ultimate control he has over all of his creations.
After Akaza's death, Doma says that he felt as if the Upper Rank had turned into a different creature before he died, and that his demise is inevitable because he never ate any women. Doma begins to cry over his 'best friend's' death, but Kanao just tells him to stop with the lies.
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.
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.
Giyu Tomioka Fulfilled His Promise to Protect Tanjiro
The Water Hashira, Giyu, survived the "Infinity Castle" arc after fighting beside Tanjiro against Akaza and Muzan. Though his sword was snapped by Akaza, and he lost an arm to Muzan, Giyu fought with Tanjiro and his fellow Hashira with everything he had.
Tengen Uzui
He is the fastest Hashira, and the second physically strongest. Obviously, then, Tengen Uzui is rather proud. He is demanding, fussy, boastful, and prone to selfishness. But he is also ultimately kind and caring, with great love for his three wives as well as the other Hashira.