After he was born, Rui had to spend 20 days in the NICU due to severe jaundice, enlarged spleen and enlarged liver. He pulled through and eventually got diagnosed with CDA1 after he was about 3 months old.
The story of Rui
Rui was born on 20th of February 2022 with severe jaundice, enlarged spleen and enlarged liver.
Rui (累) was born in a very weak and frail human body many years ago, but reborn as a Demon he is a member of the Twelve Demon Moons and holder of the lower moon five. He is the founder of his Spider Demon Family and assumes the family's youngest position as a child.
While we only saw two lower moons in action (three if you count Kyogai), Rui's the only one that was taken down by someone who wasn't part of the main cast. It makes you wonder why he was rated as lowly as he was, as you could argue, he was stronger than Enmu.
Portugal's Delta Cafes founder Rui Nabeiro dies at 91.
She is confirmed to be a transgender girl.
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.
Judging by that encounter, Nezuko is the weaker demon between she and Rui. She certainly can't defeat him on her own, and it's questionable if she can even do so with help.
1 Can't Beat: Rui
Although Zenitsu managed to overcome Rui's elder brother, it's unlikely he'd be able to do the same with Rui. Given that Rui is one of the Twelve Demon Moons, he's an incredibly powerful creature — one that almost kills Tanjiro, who's more capable than Zenitsu is when it comes to dispatching demons.
Muzan even went as far as to expect Rui to be able to defeat a Hashira by himself despite him being a Lower Rank. It was also stated that if Rui recovered all of the power he shared with his "family", he could have been a good match for the Hashira, and possibly could have been stronger than them.
Rui Ayaki (綾木 累, Ayaki Rui), better known as Rui, is a major antagonist in Demon Slayer: Kimetsu no Yaiba and the main antagonist of the Natagumo Mountain Arc. He was Lower Rank Five of the Twelve Kizuki, although it was later revealed that his true power was actually much greater.
Shinobu Kocho's tragic backstory is one of the most heart-wrenching in Demon Slayer. She and her sister, Kanae, were orphaned at a young age after their parents were killed by a demon.
The Wind Hashira has one of the saddest backstories in Demon Slayer. His mother had turned into a demon and had killed five of his siblings. He was forced to kill his own mother in an attempt to save his only remaining brother, Genya.
Introduction. Hantengu's primary form has a persona of cowardice. He was easily frightened by what occurred in his surroundings, showing traits of paranoia, fear and delusion. He was always shown to cry out in fear at even the most insignificant things.
Intelligence: At least Above Average. Though only living for less than twenty years as a Demon, Rui was a fearsome Demon who grew in strength to the point of becoming a part of Muzan's Twelve Kizuki, twelve Demons who are the strongest that server directly under said Demon King.
It was revealed by Gyutaro that Daki's birth name as a human, "Ume", was the name of the disease that killed their mother. It appears that would be syphilis, as its Japanese name is "Baidoku" (梅毒); "Bai" and "Ume" are alternative readings of the same character.
After his treachery, Kaigaku later becomes Zenitsu's archenemy. His cowardice would later lead him to his downfall when Zenitsu overcomes his insecurities as Kaigaku mocks Jigoro. Kaigaku's Thunder Breathing training would lead to his Blood Demon Arts being related to lightning.
Demon Slayers are known for their strength and bravery in battle, but not Zenitsu. Despite his cowardice, he's one of the strongest in the series. The life of a demon slayer is one of hardship.
The fact that Giyu easily takes down Rui, a demon that nearly kills both Tanjiro and Nezuko, also proves that he's a more powerful demon slayer than Tanjiro — at least currently.
Weakness(es)
Nezuko Kamado, like any other character, has her share of weaknesses that she needs to overcome. One of her main weaknesses is her inability to control her demon instincts at times, leading her to act impulsively and recklessly.
Since Nezuko is from a Sun Breathing lineage she can survive in daylight. After the final battle against Hantengu concludes she can step into daylight and many theories are available about the phenomenon. One of the theories is that her abstinence from consuming human blood is what saved her.
1 Exploding Blood/Pyrokinesis Blood Demon Art
By far, this is Nezuko's most damaging technique when it comes to fighting her own kind.
Haruka Shiraishi: Muzan's Daughter.
Muzan himself never thought highly of Daki and didn't reciprocate her devotion whatsoever, only ever talking to her to sweetly manipulate her into defeating Demon Slayers on his behalf.
It is revealed that Muzan's true fear of dying and immense desire to live and survive was due to him being born "dead," where his heart would constantly stop in his mother's womb and was assumed stillborn until he fought to breathe before his cremation.