There is no logical reason in relation to the plot that suggests why she has a horn. While fans might assume the horn grows on people with some relation to the sun, this wasn't the case for Tanjiro, who also turned into a demon. The only other reason that could explain the horn's existence is purely aesthetic.
Nezuko's body transforms as she breaks her bamboo muzzle, a horn grows out of the right side of her forehead and her body also becomes covered in ivy-like demon crests.
However, the trait that sets her apart from all other demons is the fact that she has the ability to conquer the sun, prompting the Demon King to call her the "chosen demon". Abnormal Demon Physiology: As the "chosen demon", Nezuko has several unique demonic traits that set her apart from all other demons.
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.
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.
However, she wasn't immune to the sunlight initially, as she got burned badly at first. So, in conclusion, her coming from a Sun Breathing user's lineage and not relying on human substance are perhaps the reasons for her immunity.
Pyrokinesis: Nezuko's Blood Demon Art allows her to generate and manipulate special demonic flames created from her blood that are pinkish in color.
Nezuko is at least stronger than Daki, meaning that if Muzan could bring her back under his control, she would certainly qualify for the most prestigious title a demon can hold: a member of the Twelve Kizuki. Thanks to Nezuko's remarkable strength, she would have to be an Upper-Moon.
@IsekaiCitizen Yoriichi and the kamado family are not related but the most common and logical reason for Muzan killing Tanjiro's family is revenge.
As he gives all of his blood to Tanjiro, Muzan says that if the boy survived this he would become the strongest Demon ever. Since he was the brother of Nezuko Kamado who was the first Demon to develop an immunity to sunlight and also the only one capable of using the Breath Style of Yoriichi Tsugikuni.
Zenitsu Agatsuma
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.
Nezuko survives without eating humans because unlike other demons who need human flesh to get back their energy , nezuko gets back her energy sleeping . As we see in the anime she sleeps in the box Tanjiro carries on his back .
If she took off her muzzle, she could possibly hurt someone without the intention or realising when she loses control. In the manga, Nezuko conquers the sun, so she does not need the muzzle as she can also now speak and control herself a bit more.
Nezuko is easily one of the most powerful demons in the Demon Slayer series, possibly due to the large quantity of blood she was given by Muzan. But what makes her a truly terrifying opponent is her willpower, being the only other demon after Tamayo to escape Muzan's control.
Nezuko removed her bamboo muzzle in the Entertainment District arc. When the fan-favorite Imouoto fought against Daki, she underwent a transformation that gave her a new set of powers. She became so strong that she single-handedly drove Daki into a corner.
Even 400 years later, Muzan's fear of Yoriichi remained fully intact, as simply laying eyes on Tanjiro's hanafuda earrings caused him to recall their clash.
The Thirteenth Form of the Sun Breathing Style is unique in the sense that it doesn't really have a name of its own. Rather, it's a combination of all the twelve forms present in this style, used in succession to maximize their power. This move was devised by Tanjiro solely to defeat Muzan.
The explosion, which was enhanced by spike traps, manages to injure Muzan. Before he is able to regenerate fully, Tamayo appears and uses her Blood Demon Art to keep him in place, while using a drug that can turn him into human. Using this opportunity, Gyomei Himejima appears and destroys Muzan's head.
She was ranked in 3rd place in the first Demon Slayer character popularity poll with 3,319 votes. IGN regarded Nezuko as one of the series's most popular characters and noted how her design elaborates the way she sees humans as good people as a result of hypnosis.
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.
Overall Abilities: As a Hashira of the Demon Slayer Corps, Nezuko is a very powerful and skilled swordswoman and combatant.
At 14, just a year younger than Tanjiro and Inosuke, Nezuko is very much the baby out of the four. She's also the youngest of the main cast.
It's most likely that Nezuko's flame-colored hair is a physical sign of her demon side, a reminder to the audience that she's no longer the innocent girl from the village.