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echantedtoon · 5 months

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KNY Swap Au Ramblings

I've seen a lot of others make their own versions of a swap au and I wanted to create one too just for fun. None of this is cannon, and not everyone will be swapped out and it'll have my own twists on things. And have some things added for new story elements.

Most of the role swaps I've seen are usually with either Sanemi and Genya or Gyutaro and Ume replacing Nezuko and Tanjiro. Or the rolls are swapped with Tanjiro being the demon instead(personally my favorite interpretation of this is by @yuramec). But for this I'm swapping out the Kamado Siblings for the Tokito Twins. I won't go into depth about everyone but I will give important differences to the story.

WARNINGS: Mentioning of killing, death, lose of a child, etc.

EDIT: If you don't agree with any of the placements or head cannons that's fine. This is only my take on things.

PROLOGUE:

I'm swapping out Muzan for Kagaya for this purpose. Most of the story remains the same as it did in cannon with Muzan. Kagaya is born deathly ill, he's given the medicine made with the blue spider lily, however instead of killing said doctor out of anger Kagaya is completely overjoyed and taken by the doctor's success. He wants to make MORE medicine. He wants to give this to MORE people like himself! At first the doctor accepts this. He's excited for the success of his medical treatment. However something isn't right.

Kagaya is twisted by the medicine and it's effects on his body. He begins to crave human flesh as Cannon Muzan (who I will refer to as CM), however he sees it as a greater mercy to the masses. Why live such miserable lives when you can join him? Be a part of him? Death is a mercy. Life isn't. The doctor is appalled at the way the medicine twisted Kagaya into a far worse person. (His mindset would be a similar one to Cannon Douma. Seeing it as a mercy or better fate to become a part of something bigger for the greater good overall not really seeing his twisted thinking is only harming hundreds of others and not really caring believing the end goal is worth all the bloodshed to get there.) In a fit of frustration, he attempts to turn the doctor into a demon in order to force him to make more medicine after the doctor refuses to do anymore research disgusted by the results, however as he was still fairly new to making other demons, the doctor instead dies from the infected blood. Frustrated Kagaya attempts to make the next hundreds of years perfecting his technique and turning people into demons as 'sharing his gift'. The first few demons was his beloved wife Amane and their five children.

He attempted to turn the rest of his family into demons too but that did not go so well. (Apparently it's cannon that Kagaya used to have two younger brothers). As with the doctor his youngest brother's body didn't react to him changing and Kagaya accidentally ended up killing his youngest brother. His other younger brother and their father fled and went into hiding. His father later blamed himself heavily for all of the evil Kagaya does and takes his own life. Kagaya's brother later goes on to create the demon slayer corp in search of a way to stop him. Later down the line the Ubuyashiki name is lost and replaced by the last name Kibutsuji, their bloodline cursed due to creating the first demon progenitor.

KAGAYA UBUYASHIKI AND FAMILY AS DEMONS:

He sees his demons as 'beloved children' and as such sees what they do (eating humans, killing, etc) as nothing wrong and only as a means for survival and to spread his 'gift.' Don't underestimate him however. He may not rule by fear but his voice and mind is able to manipulate and soothe most demons into submission, and he is not afraid to use force if needed. Amane and their demon children are the ones that he allows to eat disobedient demons if they're hungry and he does so with a warm smile on his face. It puts the fear into anyone who sees it if they aren't already loyally following him. He is also crazily strong physically and mentally.

Desperately looking for both the blue spider lily and the Kibutsuji family. He doesn't want to kill Muzan and his family per say. Merely to put a endless mercy to his beloved little brother's family's torment and free his own 'children' from theirs. Whether it be by turning them or by 'sending them to heaven' he hasn't decided yet. Created the Infinity Castle as a safe haven for his newly turned family and any demon deciding to live there.

Amane is his beloved spouse and is actually the one who controls the Infinity Castle in place of Nakime, and constantly rotates it keeping track of their children. She usually just blinks and any demon her husband wants is immediately teleported to them. Their children are absolutely NOT allowed to leave the Infinity Castle. AT ALL.

He created the twelve Kizuki as a way to reward his most obedient 'children' and as extra protection for himself and his family. The lower three moons are usually killed off not by him but usually by Sanemi in anger or by slayers. Otherwise he has no problem with how the Kizuki interact. Although his favorite is Yoriichi who happens to be Upper Moon One, and his most loyal and powerful demon. He usually doesn't have any trouble blending into society Thanks to his personality but he still eats, kills, and makes demons.

UPPER MOON ONE YORIICHI:

This one's sorta obvious but also an idea I haven't seen explored too often also he's not as OP as he is in cannon. Essentially everything proceeds to happen with Yoriichi the same as in cannon. I mean everything is the same except for Uta's death. As Yoriichi is late to getting back to Uta and their unborn child, Uta unexpectedly went into early labor losing the child and her own life due to complications. Unfortunately Yoriichi arrived a little too late and was devastated by the discovery of his family, but as the causes of death was natural instead of by the hands of a demon, Yoriichi does not develop the hatred for demons he has within the normal timeline. Yoriichi still buries Uta in the mountains where the blue spider lily grows unknown to everyone, and leaves to wonder aimlessly until coming across one of the strongest demon slayers at the time battling a powerful demon. Being the kind person he is Yoriichi helps him with his own sword skills where afterwards the slayer is impressed with Yoriichi's skills and invites him to join the corps. Without the drive of hatred for demons, Yoriichi decides to join instead for a desire to help others and a place of belongings. From there everything also continues as in cannon. Yoriichi meets Tanjiro's ancestors saving them from a demon and becoming good enough friends to teach the Hinakami Kagura dance, and gifts them his earrings as a keepsake. He still comes across Michikatsu and everything continues as it was.

Michikatsu's own story proceeds the same without much change. His entire backstory up to this point does not change in the slightest. His pride, his jealousy, his drive. All of it remains the same. The only real difference is when Yoriichi and Kagaya happens to accidentally come across face to face.

Because of the real driving hatred of demons Yoriichi would've previously had, and Kagaya's own nature, it would inevitably end up differently. Kagaya's compliments of his strength and the genuinity of his compliments and kindness has Yoriichi confused. He was different than all the regular blood thirsty demons that he usually killed, so why was this so.. Different. His hesitation and confusion leaves Kagaya with an opening to explain himself and to explain his twisted 'help' and Yoriichi finds himself entranced. Kagaya's talks leads the two to genuinely bond over their own personal losses and lives and Yoriichi finds himself oddly at peace listening to the Demon King's words. What if he was right? What if this new medicine could've prevented Uta from dying and had made it possible for their child to survive? What if his mother could've also been spared such a tragic fate? What if this entire tragedy could've been prevented?

Kagaya genuinely likes Yoriichi's personality and genuine drive of the same goals he has. Sure he manipulates him a little bit but in the end it's 'for the greater good for everyone'. So when he offers the haishira his blood, Yoriichi only needs a few minutes to think it over before accepting. Yoriichi as Upper Moon One is stoic, distant. Barely speaks. Somewhat twisted by the blood in his veins. He's been rejected and cast aside for so long and been dealt so much grief that it was easy for him to follow Kagaya. He has a place now, with a purpose. A GOOD purpose. He loves playing with the Ubuyashiki quintuplets and gets along with most of the other Kizuki, although during his long reign as a demon he's become numb to most feelings making him a ruthless asset on the battle field for Kagaya's purpose.

His one regret is Michikatsu.

Michikatsu's reaction to his brother ascension to a demon was rather mixed to say the least. He's angry. Enraged that his brother had not only gotten stronger, but was just handed that power essentially without even working for it as he had. (Context for that see @lavenderdrxp's character analysis of Kokushibo/Michikatsu's work ethics and character drive for this next bit.) Not to be out done, not to be bested by his brother anymore, not to allow his work to be undermined- He rejects Yoriichi's offer to join him in serving Kagaya disgusted by the thought of joining only to never surpass him for eternity and have the proof constantly living with him. So he rejects Yoriichi's offer, opting to try and kill his brother instead. It ends with Yoriichi killing his brother in battle. The death of his (for now) only remaining family member drives Yoriichi further into his emotionless state.

His prized possession is the flute Michikatsu gifted him which he carries with him. He fights using his sun breathing techniques and making six swords with his arms. After being changed into a demon, Yoriichi's body suffered some permanent damage from the side effects of Kagaya having problems creating demons. To make up for this, Kagaya gifted him six arms to replicate the movements he once originally had. In similarity to Yoriichi Type Zero.

UPPER MOON TWO GYOMEI:

Most powerful Haishira becomes second most powerful demon. Gyomei runs a (cult-) refuge in the same way Cannon Douma does, the only difference is that he actually believes what he teaches, deeply believes in Kagaya, and believes sending the helpless people that flock to him to 'Eternal Paradise' actually helps them and spares them from their tragic lives.

He fights using stone manipulation demon arts similar to Cannon Douma's ice manipulation abilities.

UPPER MOON THREE MITSURI:

Not much to say about upper three. She's very strong and flexible and uses the strength to claw her way up the ranks to just under Gyomei who she couldn't bring herself to challenge because he's too nice to fight for Upper Two. She was changed after running away from home and striking a friendship with a snake demon. Obanai changed Mitsuri out of greed and selfishness. Mitsuri clawed her way up the ranks because she heard that she could get more attention from demons and slayers if she was an upper rank. Originally joined Upper Ranks looking for a husband.... Obanai is still sitting in the sidelines trying to get her attention back on him.

Her demon arts are similar to Akaza's that she fights using physical strength and reflexes, but she can also use a charming affect to lure in prey.

UPPER MOON FOUR SANEMI:

Scary. Very, very, VERY scary. But also very protective of his younger demon brother Genya whom doesn't remember his life before becoming a demon. Sanemi and Genya were the only survivors after their own mother was turned into a demon and slaughtered their own family. Their entire life was pretty much the same until Sanemi just so happened to run into the demon king Kagaya. The king felt sorry for the two brothers and forcibly turned them both so neither could be separated again. Sanemi doesn't remember much of his human life except for the love and protectiveness he feels for his brother. Extremely loyal to Kagaya and and hot tempered. Physically wrestled Tengen out of Upper Four and wouldn't let him go until he agreed to give him the placement of Upper Moon four. The only two people who he'll listen to is Kagaya and Gyomei. Although he respects Kanae. Constantly starting fights with the lower moons and weeding out the ones he doesn't think is worthy no matter how much Kagaya and Gyomei scold him.

He uses Air blood demon arts in a similar fashion to Karaku.

UPPER MOON FIVE TENGEN:

Not much to say about him. Kagaya found him depressed after leaving his father and remaining brother after being forced to fight to the death with his other siblings. It did not take much convincing to change him. Demon Tengen changed his three wives and forcibly changed his best friend Rengoku. Is scared of Sanemi after the air demon physically held him down and forced him to give up his previous place as Upper Moon Three. Best friends with Rengoku.

Tengen fights in both numbers with his wives in ambush style attacks and by sound baced demon arts such as Urogi's screech abilities and using sounds to distract, destroy, or decoy his enemies.

UPPER MOON SIX RENGOKU:

Not much to say about this demon. He was actually forcibly turned by Tengen and doesn't remember too much about his previous life although he has glimpses of a woman who's kind with red eyes and a little flamed haired boy that looks like him sorta. Much of Rengokus positive attitude is still present but as a demon it's toxic positivity only contributing to Kagaya's toxic 'merciful' agenda. He currently is content with his place as Upper Five and gets along with most of the others. Although he has to stop Sanemi and Tengen from fighting a lot as Tengen likes to tease others.

His blood demon arts is fire based which is why he usually doesn't leave shelter if it rains or go places where water is present. Making his abilities limited.

DEMON KANAE AND SHINOBU:

The real powerful demon is Kanae who shares it with her sister Shinobu. To be honest no one is really sure where they came from or how Lord Kagaya found them. He just introduced the demonic butterfly duo one day to the rest of the Kizuki and placed them in with the others. Kanae is the much kinder of the two sisters and believes that not all slayers are bad. Shinobu heavily disagrees with that sentiment and prefers to poison her victims slowly with a smile. The sisters have two younger butterfly demons, Aoi and Kanao, and together the four of them run a laboratory for Lord Kagaya in his research of his specialized blood. They also have three small helper girls that they took in out of pity. The three butterfly girls often can be found playing with the Ubuyashiki quintuplets in the Infinity Castle.

Similar to how Cannon Nakime didn't have an official number in the Kizuki ranks despite considered a part of it, the sisters are considered part of the official Kizuki despite having an official number. It's rare that they are in fights usually spending their time doing research, but the sisters can use flying attacks, poison, flying petals sharp enough to be blades.

LOWER MOON ONE GIYUU:

Like the sisters, not much is known about where the most powerful Lower Moon originated from. Lord Kagaya brought him back and he's been tailing after his approval since. His is mostly an outcast by choice being very quiet and reserved but Shinobu likes talking to him and Mitsuri, Gyomei, and Rengoku go out of their way to be polite to him unlike Obanai and Sanemi who openly detest his presence. Yoriichi likes him well enough though. Both are quiet and don't talk too much. He finds Giyuu's character and presence similar to his own and thus likes him.

Giyuu's blood demon arts are water manipulation similar to Sanemi's wind manipulation but because of waters flexibility he's can do much more with it. A reason why Sanemi hates him and why Rengoku keeps his distance.

DEMON OBANAI:

Similar to the Butterfly sisters, Obanai doesn't really have an official number despite being considered a part of the Kizuki. Is the one to forcibly turned Mitsuri. After meeting the girl and starting a friendship with her (at the time she was engaged and he respected that despite not liking her fiance) , he eventually fell in love with her and forcibly changed her after her deadbeat fiance dumped her later eating him in retaliation. Obanai himself was changed by the very snake demon that killed the rest of his human family although he really doesn't remember, however he has a general dislike for most women he can't explain. Usually he just lounges around waiting for prey to ambush.

His blood arts are unique. He's able to fling sharpened scales from his serpent tail, contrict his victims, poison them, shoot darts of venom from his mouth, and a series of ambush snake strikes to take down his prey

LOWER MOON TWO RUI:

One of the ones I didn't swap out. In a similar fashion to Muzan, Kagaya gave RUI some of his blood and allowed him to remake his own family out of pity from his own mortal life. Not really much changes except for who kills Rui later.

TAMAYO AND YUSHIRO:

Again nothing really changes with them too much. Kagaya originally was interested in Tamayo's abilities as a doctor nevermind the fact her family tragically was killed by his own demons. Tamayo was one of the rare demons who remembered her human life and saw right through Kagaya's twisted justice agenda. She was able to mentally break free from his hold after Yoriichi's encounter with Michikatsu and witnessing the strength and driving force the Moon Haishira had endured to withstand against him.

The story from there continues as normally.

That's it for now. Might do a second drabble with the SWAP Haishira if anyone's interested in hearing more about this.

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