He has a curse mark that is slowly killing him that also makes his skin look as if it was rotting spreading down his face and covering his eyes making him unable to see, by the time of his death this curse had spread all over his body making moving nearly impossible.
As stated by Kagaya, the disease currently ailing him is the curse inflicted on his family due to them birthing the "Original Demon".
The Demon Slayer Corps' master's name isn't given, and he's instead referred to just as Master/Oyakata-sama. He's aided by the two girls from the Final Selection, and it's quickly revealed that he suffers from some sort of ailment that's rendered him blind.
Gyomei is blind, thus explaining the reason for the lack of pupils in his eyes. He was blinded due to a fever he had when he was a child.
It was then revealed that Muzan and Kagaya are from the same family which led to the Ubuyashiki family being cursed where every child born will be weak and die right away.
reason why Nezuko can't heal him because his illness is . not based on some demons blood demon. art. It's actually a curse the Ubuyashiki family is stricken with because Muzan.
Curse of Kibutsuji
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. Susamaru accidentally shot Muzan's name aloud, attempting to defend his honor with her mind clouded.
Sound Hashira
He is the fastest Hashira, and the second physically strongest. Obviously, then, Tengen Uzui is rather proud. He is demanding, fussy, boastful, and prone to selfishness. But he is also ultimately kind and caring, with great love for his three wives as well as the other Hashira.
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.
Who was the first and last hashira? Goku isn't a hashira because he is the main character in a "Dragon Ball" and he is a Saiyan. As for the "first ever Hashira"...that is unknown. As for the "last ever Hashira"...that would be Shinazugawa-san as well as Tomioka-san.
He has a curse mark that is slowly killing him that also makes his skin look as if it was rotting spreading down his face and covering his eyes making him unable to see, by the time of his death this curse had spread all over his body making moving nearly impossible.
10/10 Kagaya Is A Tactful Person
It is his ability to balance and weigh every word that he says which allows him to captivate people as brash as Sanemi Shinazugawa, or as passive as Muichiro Tokito.
8/13 Shinobu Kocho, The Insect Hashira
That being said, she's arguably the weakest Hashira when it comes to pure strength.
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.
5/14 Fastest Hashira In Running
Despite his large and muscular build, Tengen Uzui is the fastest runner among the Hashira.
He is a former member of the Demon Slayer Corps, as well as the previous Water Hashira. He is also the teacher of Tanjiro Kamado, Giyu Tomioka, Sabito, and Makomo.
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.
Tanjiro certainly did a lot of good with his Water Breathing techniques, but his ability to use Sun Breathing both gives him an edge in battle and allows him to stand out among the incredibly powerful Hashira he fights alongside.
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.
Mitsuri. The love Hashira and upcoming featured character of season 3, Mitsuri is best known for her extreme affection for everyone in the Demon Slayer Corps.
2) Sanemi Shinazugawa
His fast movement, combined with his excellent swordsmanship, makes him a remarkable demon slayer. Most of his attacks are purely offensive due to his breathing style. Being a user of wind breathing, he is undoubtedly fast.
1) Shinobu Kocho
The Insect Pillar of Demon Slayer Corps, Shinobu is undeniably the smartest individual. She might not be physically stronger than others, but her intelligence is what kept her going.
Don't go! DON'T LEAVE ME HERE! Muzan speaks his final words as he loses control over Tanjiro.
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.
Fun fact: The reason why Enmu was able to say Muzan's name out loud without dying is because they're married!