A Promise (Daki x Male Reader)

Prologue

Years before the Events of Demon Slayer

A fierce battle had been going on in the Entertainment District. A brother and sister were fighting against a Demon Slayer. All parties involved understood that this battle would be the last one for one side. The Demon Slayer was badly poisoned and on his last legs but still continued fighting. The Demons were in bad shape as well.

Gyutaro's pov

This guy really is something else. The poison from my sickles hasn't slowed his movements despite him clearly looking like he was about to die. The Sword of his is irritating as hell.

"How are you still alive?! Just die already damn you!" Daki cried out in anger only to receive silence in response.

The Demon Slayer simply stood perfectly still...wait...why is the air suddenly growing so tense?! A powerful energy started to eminate from this bastard!

"Daki! We have to finish this guy now!" I said in a...panic? I was actually panicking? No. That can't be.

Pushing the thoughts aside, I suddenly rushed the demon slayer. He still just stood there with his sword held out in front of him. Stop thinking about it and just kill the bastard!

But then...

"Shadow Breathing. Eleventh Form. Eternal Darkness"

Before I could reach him, that powerful energy flowed to his sword and he sent the biggest wave of an attack I had ever seen. Shadows completely washed over me and soon my body was being torn to pieces by a force I couldn't escape. It ended at my neck and though I couldn't see anything. I knew...it was over.

The darkness cleared and I found that I was looking at...my sister's body? He ended us both with a single technique? Dammit! I growled and was about to yell at Daki for being useless but before a word got out

"You two are siblings. It pains me to see you fighting each other. I know you don't harbor any actual ill feelings towards one another so please. Stop lying"

He spoke. This was the first time that demon slayer actually spoke to us or anybody. Daki said she had been watching him for awhile and never heard him speak.

"You two won't die alone. I soon will die as well. That is the cost of the Eleventh Form of Shadow Breathing. It means Eternal Darkness for all involved. It is the ultimate last resort."

I looked up and saw his blood covered face. His eyes were different from before. They were softer...warmer. They had been so cold and empty up until now.

Daki was beyond pissed off. So much so that she was crying her eyes out. She was repeatedly telling him to shut up and that she was pissed off. However she then said once thing that resonated with me.

"I'm scared! I don't wanna die! Please do something!"

"You have nothing to be afraid of. Even Death can't separate you two. I can sense how strong your bond is. Just wait for him when you get to where you go. He'll be right there"

The Demon Slayer was now on his knees, close to death and yet his breathing was so calm. What is this guy? Why did I feel...at ease around him now?

"Hey. What is your name?"

"YN."

"Can you promise me something?"

"Of course. What is it you wish for me to promise?"

"No matter how we get reborn. Daki and I will always end up how we were. Or at least I will. I want you to find us and help guide her off of my path. My one regret is dragging her into this. Had I not been the one who raised her, she'd probably be living a better life"

As I continued talking, tears began to fill my eyes and roll down my face. I loved my sister and I hate myself for dragging her into this shit. I was the monster! Not her! My eyes suddenly widened as I felt something. A soft hand on my face and a thumb gently wiping away my tears.

"I promise"

Two words. It took two words and it felt as though my burdens have been lifted from my shoulders. YN. Thank you. You aren't like the demon slayers before you. You are different. I will be holding you to that promise so you better keep it.