This is the real reason why Kagaya Ubuyashiki is sick in Demon Slayer.
During the first season of Demon Slayer we meet Kagaya Ubuyashiki, the 97th leader of the Demon Extermination Corps which is also known as “Oyakata-sama” and is who has followed the legacy of his family guiding the hunters and Pillars throughout his life.
If there is something that instantly catches the attention of this character, it is his face, which is totally different from that of a normal person, and even could easily be mistaken for a demon. The mark that takes over half of his face looks like a burn, while his eyes have turned whitelike its tabs, which has generated many questions about it that we are going to answer in the following information.
Kagaya Ubuyashiki’s face mark is due to a cursed disease
The reason why Kagaya Ubuyashiki has a mark on her face is because of a disease generated by a strange curse that has been genetically inherited by the members of the Ubuyashiki family, thus passing through each generation as time has passed. Until now, this disease does not have a defined namebut it consists of a mark similar to a burn that spreads exponentially throughout the body of the individual, and in the process, weakens the physical conditioncauses vision loss and reduces life expectancy up to a maximum of 30 years (spoilers below).
In fact, Kagaya reached the limit of her condition when she faced Muzan, as the mark had spread too far back then, so she he did not have the ability to move his body voluntarily and the blindness had advanced too far for him to be able to escape from the Demon King.
Children of Kagaya Ubuyashiki in Demon Slayer
Kagaya Ubuyashiki has five children., the older Hinaki Ubuyashiki who is the twin of the younger Nichika Ubuyashiki, and the younger Kiriya Ubuyashiki, Kuina Ubuyashiki and Kanata Ubuyashiki. Nevertheless, it has not been determined if the disease has affected them or will at some point in history.
Kiriya would be the most outstanding son among all of them due to the fact that he becomes the 98th and last leader of the Demon Extermination Corps after the death of his father. Furthermore, he would also be the head of the Ubuyashiki family, so the weight of the curse could fall on himalthough it has not yet been confirmed if by then the family would have been freed from the curse.
The curse of the Ubuyashiki in Demon Slayer
There are many doubts that have not yet been clarified about the curse of the Ubuyashiki family, although according to Kagaya himself, the members of the Ubuyashiki family are descendants of Muzan Kibutsuji. Therefore, the cursed disease is presumed to be a type of punishment by the godswho were in charge of cursing the lineage of relatives linked to Muzan due to having shed blood using their demonic powers and bringing monsters to a previously peaceful world.
The story of Muzan and the cursed disease
To understand it better, we have to move to the Heian era where Muzan was an ordinary human that he had been affected by a congenital disease, so his body was frail, so much so that the disease was destined to end Muzan’s life before reaching his 20th birthday.
As a last resort, Muzan’s attending physician created a medicine made from a plant called “Blue Spider Lily” to treat the disease, but the result was totally unexpected. Muzan thinking that the antidote had not worked, he followed his instincts and murdered the doctor when in fact it had taken effect, only that beyond healing him, it ended up turning him into a demon hungry for human flesh. It is here when the cursed disease would be born that affected all his descendants, who dedicated themselves to maintaining the organization of the Demon Extermination Corps in each of their generations.