Mukago x Demon Slayer reader

Epilouge

I land on my feet, I look around and I know where I'm at already the infinity castle, damnit! I look to my right and see Rengoku.

Y/N: Rengoku!

Rengoku: Y/N!

I look to my left and see someone else carrying a sword

Y/N: who is this?

Rengoku: that is my brother, he possess the same name as you, weird huh?

Y/N: right you're the one dating Mitsuri right (story on my profile)

Rengoku Y/N: yeah, but none of that is important right now, this is probably our final chance at killing Muzan!

I start walking and thinking, all we have is
and my father

Y/N: alright! Come on guys

Michikatsu runs up to us

Michikatsu: Y/N!

Y/N: nice of you to join us yoriichi would be proud

Michikatsu nods

Muzan pov

All my toughest fighters wiped out, even upper one has been turned to a human, what is going on here? Where are they getting all of this...

Y/N and all the demon slayers run in the room

Y/N: from me father!

Muzan: you son of a bitch!

Y/N: I know!

Muzan: (crap I walked right into that)

Just like that the fight begins, you jump around muzans attacks while you look to your left and see someone on the ground, it's no...

Muzan pov

These stupid humans! And to make matters worse they're with my son, and he doesn't know it yet but he's even stronger than me I didn't tell him but I'm proud of him from that day...

He walked in the sun, and it didn't affect him, he had more of my blood than any demon and the sun didn't phase him, and yet as much as I wanted to harness his power I couldn't do it, I can't kill my son

Muzan falls on one knee

Y/N: pov

I stand in front of my father on one knee

Y/N: Tanjiro...

I can't do it, I can't take down my father... as much as I despise him I can't do it...

You approach him and stick your hand out...

Y/N: father  frankly I hate you... but this doesn't mean you can't start a new, I want you to grow old with us, death is scary but it's a natural part of life... if it's immortality you seek

You hold up a blue flower Lilly

Y/N: I can make it happen but... you must change your ways. Do you swear not to kill anyone else from here on out, and live for eternity

Muzan looks at you

Crow: fallen! Fallen! A demon slayer has fallen! Kyojuro Rengoku!

Everyone drops their swords in shock and looks at tanjiro kneeling at Rengoku

Y/N: hey Y/N, I walk up to Rengoku Y/N, I'm sorry...

(2 months later)
Rengoku family had a funeral for the oldest brother Kyojuro, and eventually matsuri and Y/N Rengoku get married and has children,  even you got married, and everyone lives the rest of their lives in peace. The end

(Ps: Muzan is now human again)