Kimetsu No Yaiba: The Tale Of The Lunar Slayer!(OC X Demon slayer)

Part 10: Finale: Endgame.

This..was the final fight.
She was fighting muzan.But she was confident she could..atleast survive..
But the hashira,She couldn't NOT worry about them..She has the power of every upper moon,she definitely won't die instantly..But she's scared for the hashira.
Yu Instantly froze the hashiras in their position inside the ice barrier,And froze the ground under them,as she proceeded to send the barrier and the frozen ground far away from her,so they don't get hit by muzan,As muzan sees her taking them away from his harm,He's angered.
"Your not a normal demon,are you? Your certainly not a true demon..Your a disgusting hybrid,aren't you?"
She refused to listen to him,as she proceeds to make even more barriers to protect the hashira.
She'd then be grabbed by her neck before she could react.

"YOU WILL LISTEN WHEN I TALK TO YOU."
By instinct,Yu immediately pushed him away by blasting ice at him before she could open her eyes.
She proceeded to stare at him,And tried not to think about the hashira being in danger.
She then had an idea.
She proceeded to create 3 clones of herself using Hantengus blood demon art,All using a specific single blood demon art despite being able to use any of them.
The first one had rui and his family's demon arts,she wore ruis outfit too.
The second one was a demon slayer who wore the Urokodaki uniform,and had a Dark blue sword,and wore a mask with a flower for eyes.
The third one looked exactly like her original self,they all do but they all wore different uniforms,except this one,But she did use all the demon arts unlike the other 2.
Yu then proceeded to merge with the floor before muzan could notice there being "2" of the original,Thinking the third copy was her.
Muzan was struggling but he wasn't losing either.
Yu would then appear in the hashiras dome,as she proceeded to turn into her normal form,and she gave them all some of her blood before they could react,she explained why she gave them her blood,was to prevent their deaths.
She then went back to muzan and fought with the other 3 clones,In order to buy some time for the hashira to gain the full power of the blood she gave them.
She proceeded to merge with all the other 3 clones and used Hantengus blood demon art to grow stronger,despite creating the clones not weakening her,which would've made no difference to her power if she absorbed them,but it seems this was how zohakuten was so much stronger then Hantengu.
She was temporarily able to overpower muzan until he starts getting serious,but then she realized something..
Memories from Kokushibo would emerge,as she learns of the demon slayer mark.
And due to having absorbed him,she was now capable of using it,she Then broke the barrier surrounding the hashira,as she remembered how the demon slayer mark could spread from user to user,she was also somehow capable of making this process much faster,making all the hashira gain their marks in a matter of moments.
Muzan was losing,As when Yu had used her zohakuten transformarion,The hashiras blood had instantly gotten stronger.
Not only from the Horned demonic instinct form,but from the zohakuten transformation.
Muzan proceeded to immobilise most of the hashira besides Sanemi,giyu,And Gyomei.
She'd proceed to try to overpower muzan,But he wouldn't budge.
THIS was the demon kings full power? Why was he so much stronger then she expected? How was she still not destroying him?!
she could sense him growing stronger as the fight goes on..maybe faster then her growth.
As the fight goes on,The 3 hashira that remained awake,had been immobilised as well.she tried to fight back,but she felt like she was somehow STILL holding back..She used all her techniques in order to win.
Her blood demon arts,her water breathing,She was enraged at her weakness.
The demon horns would start growing slightly longer,as her eyes would shift from 'upper 1' to 'Upper 0.'
She noticed her attacks were starting to take much bigger effect.
She was winning..she just needed a push.
She proceeded to use one final attack with the intent of immobilising muzan enough for her to finish him.
She punched and tore apart his body before he could properly regenrate,she froze his brain so it could function less,she used her modified poison blood demon art that was modified to use Westeria-like poison.
She kept blowing him away with her water demon art before he could hit her.
She kept him stuck using her threads..
She finally managed to tear his head apart from his body,and she proceeded to freeze his neck before he could regenerate,as she start absorbing him and the body that was cut away from his head.
She struggled but ultimately absorbed him..
But the hashira..we're staring at her..with.worry,discomfort..Fear?
she'd see 2 figures from far away approaching.
But she couldn't see them properly,as her vision started to get blurry.
she didn't understand..it was as if demonic instinct had possessed her again but..she wasn't able to even SEE herself fighting..
And she was confused why she was forced into this state despite no longer being in a fight.
Yu's original self was blacked out,but her body had been controlled by an entirely different being..
She was now psychotic,Evil,And Detestable.
Like as if she was truly an evil demon.
All her transformations would wear off.
Her evolved demon form would turn off,along with zohakutens transformation.
And despite being at her base..she wasn't really defeat-able.
Oddly enough,the power ups the hashira had received from her transformations and absorbtions didn't wear off..they were oddly still in effect.(they had the buffs that Kokushibo and muzan gave,Though muzan oddly enough,only gave them A giant stat boost,but no new abilities.)
They didn't know whether to attack or defend.
Most of them only had the demon slayer mark and transparent world active.
Gyomei,giyu,shinobu,obanai,and Muichiro had the selfless state,unlike the other 4.
So they were the ones more likely to survive then the rest,being able to rid themselves of unnecessary movements.
Yu had lost control of herself,and she had started approaching the hashira,with her hands being covered in a blade made of energy,with the intent to kill.
She then started losing her calm state and had ran to approach them
but as soon as she hit something..they weren't her targets,She couldn't even see her targets.
Infront of her,she could care less,as she sensed they had her blood Inside her,and as soon as she started absorbing them,she felt 2 hands grab near her ears,As one of the 2 targets would headbutt her,making it feel like her body was covered in a glass that was shattered by the impact.
Then,the 2 targets would fall as soon as all her own blood that she sensed was in her was fully absorbed.
She then saw something that shook her to the core.
Those weren't any of the hashira.
Those were her siblings,lying on the floor,as if dead.
(Warning,If you don't like songs,this part has one,not mine,and lyrics were rearranged.)
🎶A Heart that fills up like a landfill🎶
She'd fall down to the ground.
🎶A job that slowly🎶
Trying to wake up the 2 siblings.
🎶Kills you🎶
she'd get more desperate as she starts shaking them harder.
🎶Bruises that won't🎶
The hashira would then wake up,seeing her getting desperate.trying to wake her fallen siblings up.
🎶Heal🎶
She'd then start tearing up,desperately trying to wake them up.
🎶you look so tired,unhappy,I'll take a Quiet life,a handshake of carbon monoxide,With no alarms and No surprises,no alarms and no surprises,no alarms and no surprises,Please🎶
Then,Suddenly,The infinity castle would start falling apart,And all the hashira would make a giant ice shield as Yu would still be trying to wake them up,but failing miserably.
Her hand would glow green,as she puts them on her sister and brothers holes in their stomach,closing the Hole and making their body in peak condition,but still not waking up.
Yu,after finishing healing them,still tries to heal them more to wake them up,but it was useless.
A blindfold would land on her head,as she suddenly starts to make a giant ice shield on top of the one the hashira created,One that was indestructive compared to theirs,Protecting them completely.
After the entire infinity castle had fallen,she'd notice it had became night time.
She proceeded to Blast away every part of the infinity castle building that remained,it seemed that Yu had absorbed Nakime,as she left a piece of her flesh to absorb any interfering demons before the battle,and had only recently found Nakime,she merged with the piece of flesh that absorbed her,And 2 demons would appear,Tamayo and yushiro,who was the one who controlled her,He then made her heal every injured hashira,And then he'd stop controlling her.
Upon returning to normal,she didn't even get confused or shocked from being controlled,she immediately went back to healing her 2 siblings,her tears finally run dry as her eyes looked like she cried an ocean.
Flash back to later,They'd be somewhere in a highly advanced slayer corps area made for those who aren't well,The state of the 2 siblings was odd,it was as if they were in a coma.
Tamayo had put a spell on Yu to help her get better mentally and emotionally,which did help.
Yu then had called all the hashira,asking them if they wanted to keep their demon hybrid blood,to which all of them said No,but some said they may change their minds later.
Fast forward to a week later,Yu would have created a Large infinity castle of her own using nakimes blood demon art.
She'd make a clone of herself that looked similar to Nakime in terms of the outfit,and she also covered her eyes and had a biwa,despite not having a single eye and looking identical to the original.
Yu,had worn a similar outfit to muzan when he had disguised himself as a woman,Witht he same hairstyle and a similar outfit,She also had his eyes. They were Crimson blood red.
The clone would then teleport every single living demon that wasnt an ally before she had absorbed muzan.
She'd then activate her full power,without changing in terms of physical appearence.
She'd cast several blood demon art spells that she had created.
One had given all the demons their humanity(Mentally.) back,Another one gave them their ability to survive on human food and they were no longer capable of eating humans or hungering for humans.and another had removed their weakness to sunlight,but she also cast a spell to make sure Every single one now had a very kind soul that was also filled with righteousness in order for them to not use this power for any harm,One that changes their appearance and scent to a normal humans scent and appearance,And the last one had removed their memory of being a demon,And every demon that had no remaining loved ones also forgot their memories as humans.
They were basically humans with supernatural strength,abilities,and immortality now.
She didn't turn them into humans,as that would be a lot more difficult,considering she would have to absorb the blood they would have,which would probably make her a full demon permanently,she barely stayed a hybrid after she absorbed muzan,let alone almost every single demon.
She'd then signal her copy to take them back to where they should be,And she would then have the clone teleport herself and the original to the normal world outside the castle,as she'd absorb the clone,and she'd walk to a nearby forest,and she'd fulfill her promise to herself and she'd bring back Kokushibo.
Before returning him,she'd immediately turn him into a hybrid before he could gain consciousness,Without him having a demonic transformation that doubled his power,quite the opposite actually.
He and herself both had 3 forms.
Human,Hybrid,and Demon.
Human was a form to disguise one's self from being revealed as a demon,but halves the users power,Hybrid was one's base,Which would equal how many people they absorbed + their own power,and they're immune to the sun since their skin remains human.
Demon is the same as hybrid,But 2X,but they would no longer be immune to the sun if they don't have some of nezuko or Tanjiros blood.
But for Kokushibo,Human was basically his power if he never had his demon potential,Hybrid was half as much as strength he has as a demon,and Demon is the basically his base.
She made sure of this to prevent any Possibility of bad things happening,and she'd make sure he's in his human form once he returns.
After finishing setting up his return,he'd regain consciousness.

"...! You!"
He'd draw his sword. But the notices he only had 2 eyes,as he'd touch his face and notice it's as if he was never a demon.
"What did you do to me..?! What did you do to lord muzan?!"
"It's done."
"?!"
"The fights over,your not forced to become stronger to defeat your brother or to serve muzan."
"What?!"
"You can live a normal life now,Michikatsu."
She'd give him a hug in order to support him,as he starts crying,to his confusion.
"Why am I..?"
"Just let it all out,It's all over,you can rest well for your next years."
Skip to later,About a few weeks maybe.
Michikatsu and Yu had gotten very close,and she secretly kept using her selfless state around him in order for him to feel as if his brother was still around(in a good way,Since he now sees his brother in a good light.)so he sees a little of yoriichi in her.(which is true besides her more energetic and not so quiet personality.)
The demon slayer corp had disbanded(the hashira won't die by age 25 from the mark,since they temporarily had demon blood.)Nezuko had turned into a human after Tamayo had finally found a cure.(P.S,Tamayo and yushiro are still demons but Yu had given them sun immunity using the same BDA she used on the demons,which she got by making a blood demon art that basically multiples and spread little bits of nezuko and Tanjiros blood into everyone,barely enough for conquering the sun,even after the multiplication.)
Demons and humans co-exist,and humans have no idea besides some of "their own kind" being a little bit confused with the new modern things in the world.
As for the 2 siblings,they end up waking up,But they were unable to walk from physical trauma,but they will hopefully recover.
Yu and the other hashira remained friends,infact,

she invited michikatsu to their gatherings,which at first scared and confused them,but soon they considered him a friend just like everyone else,he even helped some of them with their fighting refinement,even if the fights are over.
this..Was her happy ending.
She didn't lose anymore people. She was finally..
Happy.
Weiters Note:
(about kokushibos eyes,
he has 6 in his hybrid or demon form,but they're optional,so he could still have 2 eyes even in his demon or hybrid form,but his human form could only have 2 though.).
P.S: : the song I put was edited a little bit,If you know the song.Props to you.
and if you find any mistakes grammatically or even in how some things work,just tell me in the comments.

Now,I want you guys to know this May or May not be the end of this series,and I hope you all enjoyed the ride,I'm sorry if it's low quality,too fast or such,after all this Is my first time writing a story,and I hope you enjoy it
So for now,Cya!