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.
Her hair is long, black, and wavy. It reaches just below her waist, turning a flame-orange color as it passes her elbows, and appears to be crimped into large, straight ridges, worn side-swept drastically to her left.
Nezuko most likely has those orange tips on her hair because of the demon blood in her. Tokitou, Inosuke and Kanao (as seen in the latest cover art featuring her) most likely has coloured tips on their hair most likely because of the influence of their particular Breath Styles.
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.
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.
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.
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.
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 .
Due to two years of hypnotic conditioning by Urokodaki, Nezuko regards all humans as her family and will mercilessly attack any demon that threatens them. Instead of consuming human flesh, Nezuko regains energy from sleep and tends to become unconscious for long periods of time after overexerting herself.
Sometime between then and her next appearance in the Infinity Castle Arc, the color of Kanao's hair changes as the ends now appear tinted slightly purple before fading to a neon pink around halfway down her ponytail.
Instead of slaying her, he knocked her unconscious and placed the bamboo in her mouth to block off her ability to bite with her fangs. The muzzle prevents her from sinking her teeth into humans, but also from biting herself, either on purpose or accidentally.
When the series starts Nezuko is 12-years-old since she is one year younger than her brother. Between the first chapter and the end of chapter 5, time has gone and two years have passed. While stuck physically at age 12 because of the whole demon thing, Nezuko is 14 chronologically.
Injured Zenitsu hugs Nezuko. 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.
Toko bears a great resemblance to her ancestor, Nezuko Kamado, having the same waist-length black hair parted to the left side of her forehead, though her hair tips are much darker than her ancestor's and are closer to an actual red color than Nezuko's orange.
Nezuko is physically 12, and chronologically 14 since she became a demon in age of 12, and it already past 2 years after that time.
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.
The only demons so far to have developed resistance to sunlight are Nezuko Kamado and Tanjiro Kamado.
Later it is revealed that he married fellow slayer Kanao Tsuyuri, In the Modern World, Tanjiro and Kano had Great-great-great grandsons named: Sumihiko Kamado and Kanata Kamado.
This is proof that Zenitsu loved Nezuko and she too came to love him at some point in time. It is difficult to assume that Zenitsu loved Nezuko from the very beginning, since the two characters barely had any form of interaction.
Kanao and Tanjiro would eventually marry and start a family, having two great-great-grandchildren by the names of Kanata Kamado and Sumihiko Kamado between them.
Of course, Nezuko never consumed any human, so Daki initially thought that she wouldn't be able to regenerate. However, Nezuko quickly restores her body parts, which obviously comes as a shock for Daki. After that, Nezuko transforms into her Berserk Demon form, which is also called her "Awakened Form."
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.
Nezuko's Blood Demon Art, called Exploding Blood, allows her to ignite her blood into pink flames or even conjure it from thin air.