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Summary:

Kokushibo couldn't let his brother die. And that night, under the red moon, the demon opened his eyes.
And Muzan has to endure Yoriichi in the Infinity Castle, while he himself enjoys the life of a demon and makes friends with the Upper Moons. Or maybe he's not so useless after all...

Chapter 1

Notes:

(See the end of the chapter for notes.)

Chapter Text

- Kokushibo, what is this?! I ask again, WHAT IS THIS?!!!

This thing was laying, since it could not be called a sitting position, on Kokushibo's lap, leaning with difficulty on one hand and staring at him with huge, round, red eyes with slit-like pupils in them. Long, dark hair, which should have turned gray a long time ago, reached the middle of this something's back, red patterns of flame were spreading across its face, and most importantly - it had long claws on both hands, and two dragon horns were sticking out of its head, which definitely should not have been there, so there was no doubt about what had happened to it! Kokushibo only lowered his head, constantly glancing sideways at this something and pressing it to himself.

Dragging Yoriichi Tsugikuni to the Infinity Castle, turning him into a demon, just super!!!

He waited so long for this creature to finally die, and now Kokushibo turned him into an immortal being, and even cornered him right in the demonic citadel, why the hell had he even spared his brother's life?!!!

The demons surrounding them did not dare to move, simply staring at the Upper Moon One, who was practically kneeling in front of him - no, he was sitting, because he was holding the carcass of his half-dead younger brother on his lap, why had he even survive the transformation, how had he even stayed alive, he should have DIED sixty years ago, how did he even think of this?!!

Gyokko, the only Moon who dared to move at all, quietly crawled around the corner, out of the immediate line of sight, and began to carefully watch from there with one eye, the other demons did not move at all, clearly afraid of getting caught in the crossfire! Kokushibo looked at him with a CHALLENGE in all six eyes, hugging his transformed brother, who, fortunately, was only able to move weakly!
He should have also said thank him, that he didn't kill this thing in the first five seconds after he had seen it!

- How did you even come up with this idea?! To turn a demon slayer WITH SUN BREATHING into a demon and drag him to the Castle! What were you even thinking…

It was clearly useless to order him to immediately drop this thing, at least because it was clear from his eyes, that he would not drop it, Kokushibo only grabbed the other's haori tighter and practically growled something through his teeth. Growled at him!!!

This damn…

- Do you at least remember HOW MANY DEMONS he turned into mincemeat?!! - he practically shouted, almost breaking into furious screams - He had almost killed me and chopped me into pieces, I still have scars from his blade!!! And you think you can drag him here just because he's your brother?!! Maybe we should drag Ubuyashiki here too?!! You dragged the inventor of Breathing Stiles, the swordsman with the Sun Breathing, here!!! Why did you even…

Kokushibou only growled something else, this time baring his fangs. This time he himself choked on his scream!

- He can be a demon! - the Upper Moon One practically blurted out, the head of the newly-made demon was still almost dangling, so that his brother had to hold it! - I couldn't leave him there!

- Yeah, you couldn't leave him there, and where have you been for the last SIXTY years, why haven't you taken care of him?! - Kibutsuji retorted, rolling his eyes - He took pity on him when he met his relative! And he turned him and immediately dragged him here, as if he was expected here with open arms! I'll kill you both now!!!

Yoriichi only raised his head at him, blinking his huge, round red eyes from shock, already with cat-like pupils!

Judging by the fact, that Kokushibo recoiled back, hugging his brother, he would have had to kill the Upper Moon One too…

- One worthy reason, ONE, for which I should leave him…

- I have... I have nothing left! - Yoriichi suddenly practically sobbed, trying to at least horizontally lift his body on his hands, so that Kokushibo with a quiet cry grabbed him across the chest, he could not even move yet! - My wife was killed... I was kicked out of the Corps... I have no family... No friends... No home... Not even any tsuguko... My Breathing is gone... None of the current swordsmen can use it... My name is an empty sound! I am driven away by everyone who sees me... As if I do not exist!

He had nothing left…

Muzan froze with his hand raised, which he was about to lower in a fit of another scream. He had nothing left... And no one needs him, it was precisely the criterion, that he usually always converted people, such demons were much more faithful, than egoists or cowards, because they really gained something only after becoming demons, he always told the Moons, that if they see such a person, they should immediately transform it!

He himself had turned Gyokko like that when he was still a child dying on the seashore, he had found Hantengu in a similar state, that was how he had turned hundreds of others... Once upon a time, the boy on the futon had been like that, just desperately clinging to life, trying to gulp down air, while his parents were feasting with guests at the other end of the estate! And just like that, now Yoriichi was trying to get up at least on all fours, but he couldn't even move normally, and his breath was knocked out with every effort!

He had nothing left…

But in any case, this was not an argument for leaving him! Considering, what he had done!

- And if one day he just goes and kills half the demons in the Castle before he is stopped?! - Kibutsuji retorted, Kokushibo looked up at him without the previous threat, still supporting his younger brother. He realized that he was no longer in a state of rage, although it was not yet visible from his face and reactions…

- He will not kill. He will not kill anyone, if you accept him.

Because among people he has no one anyway, and among demons something may appear if they accept him, and don't push him away, like people and like the Corps had done, there was no need to say this, it was clear to everyone without words. Yoriichi laid his head on his brother's shoulder and looked at him with eyes full of tears and some kind of hidden joy.

The swordsman he had feared for sixty years - abandoned by everyone, a man, who had suffered at the hands of people, actually, no longer a man, but a demon, and the only thing, he had left, was his brother, to whom he was now clinging like a drowning man to a straw. Kokushibo would not abandon him either, not after turning him into a demon, which meant that trying to take his younger brother away from him now was the same as getting rid of the Upper Moon One at the same time…

And besides, what harm could come from Yoriichi, who had been dragged to the Castle in such a state, and who himself had suffered at the hands of people?! His brother had quickly become an incredibly strong demon, which meant that he, too, would probably be at least on his level, only this time he would not turn his blade against him…

If only he would step over his own pride now and leave him alive, and not throw him out into the sun.

- Kokushibo, can you guarantee, that he won’t kill anyone on the left and on the right, and he certainly won’t try to kill me?! - he asked in a deliberately cold tone, turning away, Yoriichi on his lap jerked, obviously realizing that the threat to his life had passed…

- Yoriichi won't! He definitely won't kill anyone! - the Upper Moon One promised, hugging his brother, while everyone, who had hidden crawled out of their corners…

- Okay, I let him stay under your responsibility! If he does anything against the demons and against me personally, I'll turn him into mincemeat! - Kibutsuji promised, heading down the stairs, it was time to end this half-meeting. Kokushibo was clearly smiling behind him, having received permission for his half-wittedness, or rather, having taken away his brother's life from him, Hantengu carefully stuck his head out from behind the railing, and Gyokko even carefully began to slither down along with several other daredevils. Only Nakime didn't seem to pay even the slightest attention to this outrage, she hadn't move during the entire meeting, and only her smile showed, that she was happy with this outcome!

- Thank you! - Yoriichi practically whispered loudly into his back, but it was only worth a half-turn of the head and a roll of the eyes.

What a thing to thank him for..!

- Don't kill anyone and start eating people! - Kibutsuji retorted, going down, while some of the demons, who had gathered their courage, tried to carefully approach the twins, the advice was very relevant, at least because Yoriichi was too exhausted after the transformation, and he needed to eat something to at least start moving.

Let's see what kind of Yoriichi Tsugikuni is…

Notes:

Kokushibo couldn't watch his brother die before his eyes, and he turned him into a demon, after which he actually took him to the Castle, where, of course, he received from Muzan for this.
The reason, why Kibutsuji decided to let him live, is that he felt sorry for him - Muzan in the canon had a tendency to turn into demons those who themselves suffered from people, and Yoriichi collected a whole bingo, starting from violence from his father in childhood and ending with the people, whom he once saved, and who preferred to forget him, and now he has to endure the sun demon in his Castle, sometimes grumbling about his presence.
However, the demon slayers definitely shouldn't have gotten rid of the swordsman with the Sun Breathing, since he was eventually accepted by the other side. And what this ultimately leads to will radically change the balance of power between demons and hunters.