Demons are incapable of walking out in broad daylight because the sunlight will burn them into the ashes. However, Nezuko has immunity against the sun, so she was given the name “The Chosen Demon”.
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.
Demon King Tanjiro technically is the strongest Demon and possibly the strongest character in Kimetsu no Yaiba. He's immune to sunlight. That means the red Nichirin won't affect him and nothing can possibly kill him.
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.
Yoriichi would be killed and Muzan will survive as he is Sun Resistant.
Curse of Kibutsuji
This curse besotted any who partake of Muzan's blood must be careful. The curse prevents Muzan's name from being spoken aloud, and any who do will meet a horrible demise. One demon, Susamaru, faced this reality when battling Tamayo.
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.
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.
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.
Well, in the manga, does master the Sun Breathing style. Apparently, Tanjiro sees Yorrichi Tsugikuni, the creator of Sun Breathing, performing all forms of the breathing style. Interestingly, Tanjiro sees Yorrichi using the technique through Sumiyoshi's memories, an ancestor of the Kamado family.
In conclusion, Nezuko cannot beat Akaza in Demon Slayer. In terms of power, physical abilities, regeneration rate and overall combat ability, Akaza is far superior compared to Nezuko.
The last user is Tanjiro Kamado, who learned the Breathing Style from his father, Tanjuro Kamado. Other people can learn this technique if taught by a Kamado descendant.
The Demon King Muzan was the first ever demon to have come into existence. He's the reason other demons exist as he was able to turn humans into demons. This demon has been living for over 1000 years in an attempt to find Blue Spider Lily, which would grant him immunity from the sun.
The Lower Rank 5 Demon Rui was a huge pain for Tanjiro to fight against. This demon's threads were extremely powerful and had all but killed both Tanjiro and Nezuko in battle. However, Rui was no match against the might of a real Hashira.
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.
Yoriichi was incredibly proficient in his Sun Breathing, being able to take down demons effortlessly and even overwhelm the Demon King and strongest Upper Rank.
The first demon that is said to have existed was Muzan Kibutsuji. The one who turned him into a demon was a generous doctor from the Heian Period, who wanted to save Muzan from death since, at the time, he was diagnosed with a disease which would kill him before he turned twenty.
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.
It was after Daki unleashed an attack and harmed multiple people, Tanjiro was extremely angry at this that his eyes were turning blood-shot red.
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.
Akaza was also one of Muzan's favorite demons out of all his subordinates. The reason behind this is Akaza's extreme loyalty to his master. The Upper Rank Three demon was always sent away on special missions, something the Upper Rank 1 and 2 were often denied of.
However, Tanjiro is not a descendant of Yoriichi Tsukiguni. Tanjiro is the descendant of someone who knew Yoriichi personally and was a good friend of his as well. Sumiyoshi was rescued by Yoriichi when a demon threatened his life. Since then Yoriichi often met him and they became close acquaintances.