Kagaya Ubuyashiki from Demon Slayer
Image via VIZ Media

What is Kagaya Ubuyashiki’s illness in Demon Slayer?

A very potent curse.

It doesn’t take a genius to figure out that Demon Slayer is all about demon slaying. However, that is easier said than done, as those actual demons are in no way weak.

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Eliminating even the tiniest of demons is already a laudable feat; which is why the titular group constantly hones its forces in preparation to face the mightiest of foes. But, interestingly enough, the one at its helm is not a swordsman with unparalleled skills but a dying man named Kagaya Ubuyashiki.

Kagaya Ubuyashiki has always been painted as physically pained. Despite attempting to train himself in swordsmanship, his body simply cannot endure the physical strain. And in the latest season of the Demon Slayer anime, the Hashira Training Arc, Kagaya has become too weak to even sit down and face the Hashira. So, what’s actually plaguing him?

Kagaya Ubuyashiki is cursed

Kagaya isn’t the first Ubuyashiki to suffer from this condition, and that’s because Kagaya isn’t merely dealing with a disease but, a curse — a curse so potent that it affects the entire Ubuyashiki bloodline. The curse stems from the fact that Kibutsuji Muzan, the forefather of demons, shares a blood relation with the Ubuyashiki Clan from a thousand years back.

The curse causes the Ubuyashikis’ bodies to be physically weak and continuously deteriorate. The spreading scars on Kagaya’s face are a manifestation of that curse. Now that the curse has already spread down to Kagaya’s body and hands, he no longer has the strength to get up.

Given their physique, most of the Ubuyashikis don’t live to 30. The curse is also more fatal for males, as the other Ubuyushakis have the option to escape their accursed fate by marrying outside the family at the age of 13. Even though their circumstances are quite dire, all hope is not lost. There’s a way to dispel the curse. All they have to do is eliminate the source of the curse — Kibutsuji Muzan himself. As such, the Ubuyashiki family has made it their mission to kill the Demon King once and for all.


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Christian Markle
Christian Markle is writing anime, manga, webtoon, and manhwa-related articles. Either that or he's hiding inside his hole indulging in manga, anime, and/or video games.