Aoi's survival journal. (Kimetsu No Yaiba Infection Au)

Prologue: The stages.

Note Entry : Stage 1

I was called to the butterfly mansion by an old friend. It seems that one of the Demon slayer Members have encountered and ended up infected with an unknown disease by a very dangerous Demon. Origins are unknown but I was willing to try my best to help.

Subject seems to have been slashed on the chest, the claw marks looking like they've ripped his skin

Depending on how exposed the infection is, When an individual is infected there is no sign of changes. I don't know if this is curable or not, but I want to say that there is hope.

Subjects minor symptoms such as scratching in the arms and wounded area, paranoia, and cracked lips are taken noted for.

When we asked what attacked him, he describes the events in detail. Starting with how it all started.

"Me and the group of twelve were investigating an area of where a demon was sighted. We entered the cavern to discover a black skinned rottened Demons with big antlers and a tall slim body. I noticed that it had a 22 civilians on crucifixes. It ran away in fear though"

I couldn't help but be curious, a demon with black skin and antleers. Why crucifixes? I might suggest to Ubuyashiki-San to sent out a Hashira.

" They attacked me and my squad when we tried to help them. I assumed they were demons so we fought back. A few of my squad mates actually ended up getting jumped by them. We managed to kill almost half of these demons but then one of our own attacked us. But when I was fighting one of them, they didn't look like demons. They look more dead and rottened. Like a lifeless husk. When one of them attacked me and gave me this wound, I decided enough was enough and ran. I was saved by the sun and used the opportunity to call for help."

I found this odd, Only Muzan can turn others into Demons. But from what this slayer describes to me is that this is some kind of infection. But they are still affected by sun light.
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Note Entry Title 2: Stage 2 day 12

From my request, Ubuyashiki sent out one of his Hashira's to go find the demon that has infected the slayer. But both he and his Kasugai crow ended up going missing on his search. Which grew concerns in the Corps but isn't the matter at hand so they sent out Tanjiro, Nezuko, and his friends to the location to investigate.

The fastest way for them is by train. So I'm Taking note of their next train station so if they go missing I will know where to investigate.

"Mugen Train"

The individuals condition had gotten worse. The color in their skin has gotten more pale, their heartbeat has slowed, and there pupils aren't reacting to light.

Hunger has decreased and their mental state is worsening. They described as if "something was chewing his gut from the inside" The Kocho sisters and I tried our best to examine this. But before anything happened The Kocho's sisters assistant with the twin tails came in saying that a Kakushi with the same mark came in seeking help. They were in the same stage process but seemed off, so I'll study their conditions.
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Note entry title: Stage 3 day 14

The Kakushi was killed ruthlessly by the wind Hashira. He said that the infection was spreading all over so he isn't risking Kanae's Kocho's safety. But what made it more horrifying was that after he rushed the Kakushi's heart, she came back to life all rabid like. This Time Shinobu Kocho killed the Kakushi by running her wisteria poison. We'd then dragged the corpse outside and see the body disappear into ash.