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Prophecy's Child

Summary:

Kamado Tanjirou does not exist.

He is not the older brother of Kamado Nezuko, a demon who does not and has not eaten humans. He is not the apprentice of Urokodaki-san, and does not learn Breath of the Water. He is not best friends with Zenitsu and Inosuke.

Kamado Tanjirou does not exist in this world, but he exists in another.

(Or: An AU where Kamado Tanjirou is a time traveler, and must stop the death of humanity before it ever happens again. He does not exist because if he did things would get a lot messier.)

Notes:

Okay so I have been following the Kimetsu no Yaiba manga for a very long time. I kinda forgot about it until I heard about episode 19 of the anime and how good it was.

Holy shit I'm so happy I checked back in, because man did it rekindle my love for this series. I began this fic this morning and just finished it. The idea came to me as I reread the manga once more, and I couldn't shake it.

Enjoy!

(See the end of the work for more notes.)

Chapter 1: Scroll of the Savior

Chapter Text

The savior shall come,

Heralded by white and red,

Draped in green and black,

Injured and scared,

To save the hunted whom

Would not have been saved

By any other.

-- Anonymous Fortune Teller, circa 1703 (Edo Period)

 

Kagaya saw the scroll for the first time when he was five years old. He’s sickly, one of the frailest children that the Ubuyashiki have ever had, and is constantly being monitored. As he walks down the simplistic yet elegant hallways for the first time, the guilt deep in his heart grows larger as he sees injured swordsmen and women walking down the halls. 

 

He remembers just last year when he had attempted to wield a sword in secret. It was just a wooden one, a training sword, yet after just ten minutes of mock-battling his muscles were about to give out, his lungs felt like they were collapsing, and his body became feverish. He remembers the tears in his eyes and the hiccuping sobs he had as he was bedridden for the next week. The shame and guilt mixed together into a deadly cocktail inside his heart.

 

So as he walks down the hallway, he keeps his head down, his smiles ready, and a string of kind words at the tip of his tongue. They pass countless demon slayers, and he takes care to greet each one. His mother, who guides him through the confusing building, smiles warmly at him every time. 

 

“Kagaya-chan, that was a very nice thing you said to Aiko,” his mother says, as they round yet another corner. He blushes but doesn’t say anything, his footsteps pattering along the tatami floors. He almost bumps into his mother as she stops abruptly in front of one of the various decorations on the walls. Kagaya cranes his head to try and read the scroll, the elegant calligraphy making his brain twist slightly.

 

“Mama? What does this scroll mean?” he asks finally. His mother smiles down at him, before picking him up and moving themselves closer to the scroll. When he’s this close he can see the texture of the paper, and knows that it’s very high quality, the type of stuff that is only used on the most important documents. 

 

“This scroll is the prophecy of our savior from the demons,” his mother answers. “Some speculate that he’ll come when the fight against the demons is strongest.”

 

“Do you think that I’ll ever meet him?” Kagaya says excitedly.

 

“I do hope so,” she says. “Although perhaps it’s best if you don’t.” Kagaya turns his head to look at his mother in confusion.

 

“Why?”

 

“Well, if the rumors are true, then I would like you to be able to live a life without worry. The savior will surely be a sign that the battles to come will be much harder,” she whispers into his ear, eyes sad. “Too difficult for humans to come out unscathed.”

 

“Hm,” Kagaya says. He doesn’t like the look on his mother’s face, tired and resigned.

“No more of this boring talk,” she says suddenly, face breaking into a grin. “Why don’t we go find you father and have lunch?” His mother sets him down but keeps her hold on one of his hands.

 

“Okay,” he says, following her out of the hallway. He turns to look at the scroll only once before they round the corner, cutting off his view.

 

Kagaya thinks about the scroll a lot. More specifically, the contents of the scroll. He imagines what the savior looks like. He doesn’t like the fourth line much, for he can’t imagine that their savior could be weak enough to be injured or scared, so he usually passes over it. 

 

He imagines that the savior is some kind of god. He asks his parents for all the gods they know, yet can’t find one that seems to fit all of the details. All of them seem to represent things, and are never mentioned to be draped in green or black.

 

He thinks that they might be a spirit, a former demon slayer, that simply can’t stand to watch the suffering of humans.

 

He imagines and waits and hopes for the savior as more and more demons appear and less and less demon slayers come back. He prays to the gods for the savior, then prays to the savior themself. He cries as his father dies, and then his mother, and then his siblings. The day he takes up the mantle as the head of the Demon Slayer Corps. he prays for hours.

 

The savior doesn’t come.

 

He attends countless funerals. He comforts family members, gets yelled at, sends people out on more and more missions and feels the guilt in his heart stab ever further.

 

The day that the savior does come is the day that he doesn’t pray for him for the first time in fifteen years.




Ah. Another one, thinks Giyuu as he passes through the woods of a small town. He hears the townspeople whisper of death and demons, and while he normally wouldn’t pay any heed a trail of blood leads him away from his path. It’s fresh blood, no older than a few minutes, so he rushes forward to the scene, following both the blood and the sound of a scuffle.

 

He is met with a strange scene. A demon in a pink haori stands over a figure lying on the ground, obviously trying to eat them. The human seems to be yelling at it to come to its senses, yet Giyuu knows that it’s futile.

 

The savior shall come,

 

He doesn’t spare a glance at the human before lifting his sword and striking, only for it to go through the air. He blinks in surprise; there’s no way that the demon is any older than a day. It shouldn’t have been able to dodge. He glances around, takes in the snow, falling ever so slowly, and the drops of blood that had given the demon’s location away.

 

The boy.

 

Heralded by white and red,

 

The human kneels over the demon, as though attempting to protect her. On his forehead is a peculiar birthmark, stark against his pale skin and long burgundy locks. There’s a small cut on his right cheek and he wears peculiar earrings depicting a rising sun. His haori is tattered and old, a checkered pattern over a -

 

Demon Slayer uniform? Giyuu thinks, then abandons the thought. No demon slayer would ever protect a demon.

 

Draped in green and black,

 

“You should step away from it,” he says, lowering his sword but not yet relaxing his stance. He knows the boy’s type: brash, idealistic, and naive. The sooner he comes to accept reality, the better. “She’s not human anymore. Any second now and she’ll try to kill you again,”

 

The boy stays silent, staring straight into his eyes. Giyuu refrains from flinching. It’s then that he sees the reason why his haori is so torn; multiple cuts and bruises are visible from what little skin the boy is showing, and he can see a gash that runs long across his chest. “Why are you  protecting her?”

 

Injured and scared,

 

“D-Don’t,” the boy says, voice raspy as though he hadn’t had a drop of water in days. Giyuu imagines that it must feel like razors in his throat. “Don’t… kill her.”

 

To save the hunted whom

 

“Why not?” he asks. “If I do not kill her here she will kill others.”

 

Would not have been saved

 

“Because… ” The boy stops and coughs harshly, shuddering through his whole body. “Because… ”

 

Giyuu stops listening, and instead slips past him in order to quickly cut off the demon that’s beginning to come to --

 

But his blade is stopped by a black nichirin sword, with the word Destruction written on it.

 

By any other.

 

“Because… there is… a, a cure… ” the boy says, before passing out.




(It’s only when he discovers the nature of the demon girl, and how protective of the boy she is, that Giyuu recollects the first day he had seen the Scroll of the Savior.

 

He remembers Oyakata-sama reading it to him, the lines obviously memorized, and feeling bitter and angry at the so-called savior. How could one call themselves a savior, if they watch as so many demon slayers, were (-- as Sabito was) killed? How could they be so vain as to only come when the fight will reach its peak?

 

But he keeps his thoughts to himself, for he knows that Oyakata-sama prays every day, that the Mizunotos’ faces when they hear about him light up with hope, and that the only reason people continue to fight is the fact that the savior of mankind will surely arrive.

 

It’s only when the boy is unconscious: the red blood, standing vividly against the snow; his checkered haori and the uniform that he now definitely recognizes as the one of his back; and the countless injuries lining his body, restricting his movements and most likely the reason that he couldn’t kill a low-level demon like the girl.

 

Either it was his injuries, or he really was telling the truth.)

 




“Caw! Message from Tomioka-san! Caw!” the crow shouts, landing down next to Kagaya. “Urgent message! Caw!”

 

“Thank you, Takeyoshi,” he says, accepting the letter with a frown. He hopes that it isn’t a sign from the gods about his failure to pray yesterday. Yet when he opens the letter he has to read it over again multiple times, mind not comprehending. When he finally finishes he registers his wife wiping away his tears, a smile fixed onto his face. 

 

Dear Oyakata-sama,

 

Yesterday I met a boy named Kamado Tanjirou on the Misty Mountain. A trail of human blood on snow led me to a scene where a female demon was trying to devour him. He was draped in a green-checkered haori over a black Demon Slayer Corps. uniform, with various injuries that were hindering him. 

 

He was obviously weakened greatly yet he managed to prevent my killing of the demon by deflecting my sword with one of his own, that had the kanji for destruction on it. It was definitely a nichirin sword, and was a pure black color.

 

He told me that he knew of a cure for demons before passing out. The demon with him protected him before she too fell asleep. I need not tell you what I think this means.

 

I am currently heading to headquarters with them. Neither have awoken as of yet.

 

-- Tomioka Giyuu, Water Pillar.

 

He drops the scroll and calls for a pillar meeting.