In the shadows waits for an evil creature wanting to devour human flesh. Without it, the demon will become weak, which is extremely dangerous in their world. Tanjiro Kamado thought this was the fate his sister would have after being infected by a monster, except her transformation was a little different.
After grabbing his sister Nezuko, Tanjiro raced to the village to get his sister's help. It's at this moment when Nezuko attacked Tanjiro, at that moment that a demon slayer appears, Giyu Tomioka. He tries to kill Nezuko, claiming no chance for her, but something strange happens. Nezuko defends her brother; it is clear that Nezuko and her demon half were battling. One craving the flesh of those around her, the other wants to protect her older brother. This is just the first of many differences Nezuko has with other demons.
She's Different
During his journey to save his sister, Tanjiro travels to Sakonji Urokodaki, a retired demon slayer, to train. During those two years, Nezuko slept, never waking. This is extremely strange because demons don't do that. Urokodaki theorizes that perhaps instead of eating humans, Nezuko is attempting to gain energy by sleeping. This means Nezuko can help Tanjiro on his missions, but when she does need to regain her strength, she'll sleep for extended periods, making her vulnerable.
Another thing that makes Nezuko stand out is her fighting ability. As a young demon Nezuko is powerful and learns fast. She shows this when fighting against Susamaru. The two battle it out, kicking Susamaru's ball back and forth at first, Nezuko's food is blown off, but after regenerating, she can keep up with Susamaru. Even nearly hitting her in the head with the ball. Nezuko's powers don't just stop here. The more she fights, the stronger she gets, it would seem. When fighting against Daki, she grows in size and strength, going into a berserker-like state. She rapidly regenerated her parts and used her blood demon art to ignite her blood.
The one thing that makes Nezuko stand out the most is her desire to protect people; when fighting Susamaru, Nezuko fought to protect Tamayo and Yushiro. At the time, she saw them as her family. Something Urokodaki did to help prevent her from devouring people. Nezuko no longer considers all humans as her family at the end of season one. Instead, she wants to defend and protect them. She shows this when she refuses to attack Sanemi, even after cutting himself and exposing it to Nezuko.
What Does This Mean?
Demons have been plaguing the world for millennia, and as far as the Demon Slayers know, nothing like this has ever happened. There are demons like Tamayo and Yushiro who have their blood lust under control, but they still need blood to get energy. Nezuko is extraordinary and one of a kind. So, what does it mean?
Well, some might take it as a sign that the era of demons is coming to an end. Even if the slayers kill Kibutsuji, perhaps more monsters will start to turn out like Nezuko. If this is the case, the slayers won't have to worry about demon attacks. They might even be able to team up with other demons to stop Kibutsuji. Though this is uncharted territory, so many of the Hashira are hesitant toward Nezuko. They've been trained to believe that all demons are evil, but now there is one that proves those ideas wrong.
Perhaps some slayers will begin questioning what they are doing. Nezuko shows that some demons might still have a part of their humanity left within them. If this is true, how many were killed before they had a chance to prove themselves? This thought could be tormenting to some. Then again, most probably just see Nezuko as an anomaly.
Though for Tamayo, Nezuko represents hope for demons. She could be the answer to everything that she has been looking for. With studies from her blood, and the blood from the Twelve Kizuki could potentially find a cure for demons. This is possible considering demons are made not born, almost like a blood illness that transforms the host. Except Nezuko's body reacted differently with the illness, so is there something in her body that caused her to react differently than other demons? This is possible, but more likely is that Nezuko refused to lose herself to this. Before turning into a demon, Nezuko adored her family. This love for them kept her from losing herself to the madness, kept her from devouring Tanjiro. Her desire is to protect what little family she has left, but the more she and her brother journey fighting demons, the bigger her found family will become. Making Nezuko stronger as well, because there are more people who need her.