After all, Giyu has won against much stronger demons than Nezuko. Rui is just one example of this, and viewers can assume that the Water Pillar has brought down others who boasted the same amount of power.
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.
Giyu was injured after a Demon's attack and was saved by Sabito, who defeated nearly every Demon on the mountain. However, after the week went by, it was revealed to Giyu that Sabito was the only one who died during their selection.
This willpower is also what helps Nezuko truly utilize her Awakened form, to fight more efficiently. While she might not be as powerful as Muzan himself, her overall strength makes her easily comparable to an Upper rank demon.
At one point or another in the manga, all nine Hashira in Demon Slayer encountered an Upper-Rank. Of the three Hashira who were killed by Upper-Ranks -- Rengoku, Shinobu and Tokito -- Shinobu was the only one who was killed almost instantly when she encountered Doma, Upper-Rank Two.
Nezuko's regeneration speed matches that of an upper moon, and later it's mentioned that it surpasses the regeneration speed of one of the upper moons. Also, Nezuko has shown to be stronger than an average demon before, when she kicked those strong demon balls for example.
Nezuko isn't like other demons, which is how she was given the name "The Chosen Demon." The reason behind this is because unlike other demons, she can actually walk in the sunlight without getting burned.
Sabito was indeed stronger than Giyu. He spent the entire final selection saving his fellow demon slayers. Giyu admitted that if Sabito survived the exam, he'd likely be the Water Pillar instead. In chapter #131, Tanjiro became tasked with convincing Giyu to participate in the Pillar Training sessions.
Fans have wondered whether Zenitsu ever got to realize his dream of becoming a Hashira at all. Unfortunately, the answer to this question would be, no, he did not. Zenitsu, along with Tanjiro and Inosuke got way stronger than average corps members with training.
Tanjirou's younger sister Nezuko, having been turned into a demon at the age of 12, returns to action in Demon Slayer Season 2: Entertainment District arc. However, chronologically, she is now 14 years old.
Tanjiro's rank in the Demon Slayer Corps is Kanoe, the fourth up from the bottom. He doesn't receive a higher rank for the remainder of the series. His rank is specified during a conversation with Inosuke held during the Entertainment District arc.
Tanjiro decapitates Akaza with the Hinokami Kagura: Setting Sun Transformation. Akaza was bewildered, wondering how Tanjiro did not have any fighting spirit, comparing this feeling to fighting against a plant. He acknowledges that Tanjiro surpassed his speed.
Gyomei Himejima is the strongest Hashira in Demon Slayer. This fact has been established in the manga as Tanjiro, Inosuke and Zenitsu all agree that he is the strongest member of the Demon Slayer Corps. His strength was showcased during the fight against Kokushibo.
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.
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.
Like all demons, Nezuko has a special ability called a Blood Demon Art. Hers is referred to as Pyrokinesis, with which she conjures bright, pink flames. Nezuko's ability is devastating for other demons, as her flames have the power to cancel out other Blood Demon Arts.
'Demon Slayer: Kimetsu no Yaiba' chapter 195 reveals why Muzan dreaded Yoriichi, Nezuko turns into human-demon hybrid? The “Demon Slayer: Kimetsu no Yaiba” chapter 195 release date is just a couple of days away.