according to Urokodaki that nezuko regain her strength by sleeping. other demons gain there strength by eating humans. so as long that she sleeps she gaining more and more power.
Refusing to feed on blood initially made Nezuko weaker and gave her a greater gap to overcome when fighting other demons, but her willpower later contributed to huge power boosts during several battles, most notably when she used her awakened form for the first time when fighting against Daki, an Upper Rank demon.
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.
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.
Nezuko takes her demon transformation a step further when she goes into berserk mode. We see horns come out of her forehead and vine markings wrapped around her body. She is at her most powerful in this form but her demon side starts to take over and she would need human blood for nourishment.
Nezuko has several powers, including regeneration, superhuman strength, growing and shrinking rapidly and a blood demon technique called Exploding Blood (爆血, Bakketsu) that causes her blood to burn once it leaves her body.
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.
Zenitsu Agatsuma
Upon seeing her for the first time, Zenitsu falls in love with Nezuko at first sight. She apparently views Zenitsu as a "weird dandelion" and did not initially seem to reciprocate his feelings. Although the two are rarely seen interacting together, Zenitsu treats her with affection and care.
Most importantly, Nezuko upholds a vow of silence by remaining mute throughout the series. The muzzle serves as a representation of Buddhist practices. First, it gags Nezuko, preventing her from speaking like a Buddhist monk's vow of silence, but it also is there to suppress her desire to eat humans.
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.
Nezuko doesn't stand a chance against the Upper Moon 3
Nezuko is undoubtedly a strong demon in Demon Slayer and she proved her strength repeatedly. One situation that really displayed her true potential was the fight against Daki. She underwent a transformation and thoroughly overwhelmed the Upper Moon 6 demon.
Her most prominent trait 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.
Moreover, while she was asleep, Urokodaki performed a unique hypnotism on Nezuko, making her believe that all humans are her family and she must not hurt them in any way. With her immense fondness for humanity, Nezuko broke out of Muzan's control, becoming free to do anything at her will.
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.
Nezuko doesn't have a rank. Not all Demons had ranks in Demon Slayer, and since Nezuko was never an ally of Muzan's, she never had a rank in the series.
Nezuko Has Suppressed Her Consciousness
Frequently, she is pictured carrying or soothing smaller siblings, clearly taking on a maternal role at a young age. However, after being transformed into a demon by Muzan Kibutsuji, the Demon King, she quickly regressed in mental age and maturity.
The now-iconic bamboo muzzle serves as a way of stopping Nezuko from using her teeth, and also keeps her from tasting human blood, which would cause her to lose control of herself.
However, during the second season of Demon Slayer, she underwent a transformation and developed a horn, and her body resembled that of a grown adult. This seems to be her awakened mode and could be her true demonic form. There is no logical reason in relation to the plot that suggests why she has a horn.
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. It is shown in the manga chapter 130, She has walked in the sun.
The young Tanjiro is not only one of the greatest demon slayers, but thanks to his kind nature, he's also one of the most honorable characters of the series. Tanjiro not only showed selflessness and love towards his sister and the people he cared for but even showed kindness towards his demonic enemies.
Nezuko Kamado
Zenitsu also protects Nezuko multiple times when she is in danger, evident during Zenitsu's first meeting with Inosuke Hashibira and the battle against Enmu in the train. Eventually Zenitsu and Nezuko would marry and start a family as evidenced by their descendants.
Later it is revealed that he married fellow slayer Kanao Tsuyuri. In the Modern World, Tanjiro and Kanao had descendants named Sumihiko Kamado and Kanata Kamado.
If Nezuko were to taste blood, it's likely that she would lose control completely, forcing Tanjiro and other demon slayers to kill her. So the bamboo gag really protects Nezuko as well as the other humans the slayers may encounter on their journey.
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.
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.