A single action can bring about great change. Whether thought out or heat of the moment, an action has a reaction. And that reaction has a consequence, sometimes more far reaching than ever thought possible.

So what would happen if, in his final years, the First Breath User wrote a letter?

What would happen if his Brother-turned-Demon read it?

What consequences would happen, and what would change?

A butterfly flaps its wings and a monsoon forms. The dragon spins and eats itself over and over and over again.

All because of a single letter, the world will change.

And Hinokami laughs.

'My Brother, do you know what the hardest part of you becoming a Demon was?

It wasn't the mocking of the Corps, the calls for my life by the Hashira, or being banished and struck from the records to never be remembered even as they used that which I had taught them.

The hardest thing was how I never saw it coming.

Despite the immense power given to me by the gods, I could never see the world as you did. Never enjoy the world as you did because of those 'gifts'.

You, my Brother. Who never failed to explain the social cues and veneer of Nobles that I never could understand. Even when it flustered you, or put you in a difficult situation with our Father or those others around us.

I am aware that I don't often understand how and why other people act as they do and not just follow their heart.

But you, Brother, never hesitated to.

When seeing me spelled punishment for you, should you have gotten caught. You taught me how to swing a blade in secret, in the snippets of time you could slip your tutors, regardless of the consequences.

And when even that was taken from you, you gifted me something you had crafted with your own hands should I ever need help.

That day when I fought your instructor, and found how I so loathed the feeling of hitting another living being, you simply said that you would get strong enough for the both of us.

Was it when Mother died and I left that you grew to hate me?

How Father wanted me to inherit instead of you because of me defeating the instructor that day? Was that how it started?

Or was it because of the so-called 'gifts' I had been given?

What other's called a blessing, felt more like a curse.

My Brother, I never wanted to be a fighter.

I never wanted to use my 'gifts' to hurt others.

I never wanted to be the first of a Kami's lineage

I simply wanted to stay by your side.

Brother, what do you do when your body is made for battle, but your heart is not?

Brother, what should I have done?

What was my purpose had I not fought?

For a time, I had lived as I wished. No fighting, no bloodshed. Just me, my wife, and our yet-unborn child.

The Kami did not seem to agree.

Brother. I had a single goal in my life. To protect those I cared for, to heal them when they were hurt.

I failed that.

My Wife slaughtered, our child torn from her womb and left to suffer a cold, lonely death.

Had I been just a little faster, had I not stopped to help that man on my way home, perhaps they both would have lived.

That day, my purpose changed.

To kill Kibutsuji Muzan and avenge all those who had suffered because of him and his Demons.

My Brother. I failed that goal as well.

What is the purpose of my power, these so-called 'Gifts' granted to me by the Gods if I failed everything I tried to achieve.

My Wife and child dead, Muzan living on, the Corps turning their back on me despite all I did for them, all I sacrificed so that no one would have to fear the dark. And my dear Brother turned into one of Muzan's Demons.

What is the point of living if you lose everything Brother?

Brother, what did I do wrong?

Did I not show how much I cared for you?

Did I not try hard enough to protect others, not give up enough towards that goal to matter? I taught the Corps varied ways of Breathing to strengthen them in ways they could handle because my own was too strenuous on their bodies. I gave them all they asked for and more. Was it still not enough?

Did I hurt you and turn a blind eye because I could not see the surface as you did?

Was it because of this Curse that masquerades as a Gift?

My Brother, do you hate me for these 'Gifts' as much as I do? These 'Gifts' that felt like chains, preventing me from seeing as you did, as you do. From experiencing the world as you do.

I carried on despite the way those chains tugged and pulled because there was still someone I cared for. Someone I could still protect.

Someone who still gave me purpose in life and had been the first one I had cared for, had loved. Even before Mother.

Before I knew who my Divine Father was.

Someone who I loved just as much as my Wife and child, perhaps even more.

I thought you had loved me in return as well.

When it was just us, in those fleeting moments during the day, and hidden hours of the night, you were so expressive of your emotions. Showing them for the world to see. Showing them where I could not, because I could not. Caring for me when Mother was unable, and the servants unwilling. You protected me, talked for me, fought for me. And I looked up to you then.

I think I still do now, despite how it hurts.

Perhaps I looked up to you so much, loved you so much because on some level, I knew you didn't feel the same.

You always pushed yourself Brother.

Pushed on despite your limits, ignoring your own health and needs in pursuit of your dreams.

Growing stronger, and stronger.

But also colder, and more closed off.

Instead of showing your emotions, you bottled them up, even around me.

Perhaps that is why I never noticed how you felt all this time. And still fail to find where it started.

Was it all my fault Brother?

What could I have done different, done better, if time rewound itself and placed us back then?

Is there even anything I could have done?

Or was your hate for me so all-encompassing even then?

Perhaps I was a weight, dragging you down Brother. One you took care of out of obligation, that I mistook for genuine care.

All those times you scolded me for being out in the rain. For chasing after a wild animal that could have hurt or killed me. For forgetting to eat for days on end.

I took and took and took, and never gave back.

I was a nuisance. Something that took up so much of your time that could have been used better.

It took me all this time to piece together why you loathed me so.

My Brother.

I am sorry for being a burden.

I am sorry for not being enough.

I am sorry for Father wanting me to take your place.

I now know that you hated me, and I should have avoided you as Father had wished.

That you hated me even speaking to you, how my voice grated on your ears.

I am so sorry, my Brother.

Because as selfish as I am, I can never stop thinking about all those moments we had alone when we were children, all those times we spent by each other in the Corps. Because all that time you were suffering silently and I was, for once in my life, blind to it.

I will always look up to you, despite how it hurts because you are my Big Brother.

You took care of me despite hating me more than anything else in the world.

And I am so sorry for loving you despite having figured out how much you hate me too late.

I am sorry for being such a sorry, sad excuse of a brother.

Of a human.

I am a man of no worth.

And for that, Nii-san.

I am sorry.

I will never forgive myself both for both failing in all my goals in life, and causing you suffering.

I am so sorry Nii-san.

I am sorry for loving you.

Yoriichi'

Kokushibo stared at the time-worn and water-stained paper that had fallen to the ground along with the stupid, near-useless, hand-carved wooden flute the Demon had given his brother 80 years ago.

The paper was innocuous and unaddressed, but despite this, it was seemingly mocking Kokushibo. There was no doubt unto whom it was addressed. Why else would Yoriichi carry it around in the same pouch as that stupid flute. Hatred has the Demon briefly contemplating just outright destroying the letter, unread. Because it was no doubt filled with moral righteousness, to apologize for how killing him was the right move. But some remnant of courtesy from being a Daimyo and a warrior stayed the Demon's hand. Here were the last words of Yoriichi, both a respected and feared Slayer and warrior… and the Demon's younger brother. Giving an uncharacteristic sigh, no matter how soft, the Demon bent and grabbed the paper. Not quite harsh enough to leave its contents illegible, but enough to leave further damage to the already worn paper. Opening the letter with a quick movement, the Demon began to read.

As the Demon's six eyes progressed through the letter, the hand holding it spasmed and shook. Tears began gathering in the eyes. Knees gave out and hit the soft, grass-covered and blood-soaked ground. Katana following not a moment after. Oblivious to this, the Being continued reading. Skipping over, and backtracking. Repeating sections, lines, and words as disbelief refused to let the information settle. Like a blade too long for its sheath, or a misshapen timber joint being placed together wrong. The Being began to shake as the end of the letter was reached.

Yoriichi… blamed himself? Hated himself? Had thought himself "nothing but a failure", and a "Person of no worth"? Yoriichi loved him? Yoriichi, who never looked shaken, panicked or disturbed by anything. Not even the revelation of what the mark was doing to their comrades, would do to them. The thoughts refused to stop swirling. A howling blizzard that refused to let anything else through.

The Being's brother, loved him? Had loved him before anything or anyone else if the letter were to be believed.

Had Yoriichi truly lost so much? Given up so much, just to make other's lives a little better?

He… had no idea. Had not known. Had always thought of Yoriichi as a Tennin. A pinnacle of innocence and kindness despite the blood of Demons that stained his hands and blade. Ko-Mich-Kokushi- had always viewed Mich-Ko-M- as all that was rotten with the world.

He had always envied his brother because of it. Had quietly seethed with it. For Yoriichi could never do any wrong. Who was perfect, always thinking such perfect thoughts, and never suffering. But, that wasn't true, was it. The hand holding the letter, nearly tearing it with how much it shook, dropped. The letter, the cause of it all, fluttering gently down and landing on the trampled pampas grass. Kok-Mi- had had no idea. Yoriichi had suffered. Suffered, and sacrificed, and gave, and loved to everyone he thought needed it. Never asking for anything in turn from anyone. Not even Michikatsu. Yoriichi, had loved Michikatsu. Despite his imperfections, his mistakes. And he, despite everything, despite his hatred, loved him back.

Air that Michikatsu no longer needed came rapid and shallow. Sapping strength and coherency as he folded over and lay his head on the ground, as if it was the only thing holding him up. Tears finally spilled over and dripped onto the ground, onto his lap, onto the letter. Clawed hands shot up to grab the letter and shield it from his tears, nearly tearing it in two in his haste to shield the precious, fragile thing. 'That wasn't water damage, it was tears' a small part of himself processed.

What was he supposed to do with this new information? It was already too late for him to join his Brother, too much innocent blood stained his hands for him to ever be allowed to rest with his Brother. Not that he deserved it in the first place for being so blind to Yoriichi's suffering. Self-destructing there and now was out of the question, regardless of how much of him keened for it.

Taking a shaky, stabilizing Breath. Michikatsu sat up and stared at the unassuming paper cradled gently in his hands. His eyes flicked over the letter as he wondered what he could do. Thoughts slightly slower, and emotions a tight knot in his throat. Michikatsu's gaze froze on a single line. One hand dropped down and grasped his katana, sliding it into place on muscle memory more than genuine thought. 'Kibutsuji Muzan,' even in his thoughts it was a low growl. 'No matter how, no matter when, I will find a way to kill you. And when I do, it will be for my Brother.' Standing, he looked around at the clearing. Marred more by his rage at being unable to land a blow on his brother while he drew breath more than their actual fight, if it could even be called that. Pocketing the letter and broken flute Michikatsu stepped away. Taking one more shaky Breath, he whispered, "You deserved better than this Yoriichi… Forgive this foolish Brother of yours. This one thing… will be set right." before breaking into a run.

He knew just where to start, but he needed time.