Rui x Fem!oldersister!reader
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Y/n was a girl who had a younger brother named Rui.
Rui was a very sick boy when he was human he had a weak body and he can't come outside.
One day Y/n went out to buy dinner for her and her family also Rui.

When Y/n came back..
Y/n Pov:
I was walking back to our house after buying dinner for my family and I. While I was walking back I heard a scream I rushed to our house to see my parents dead.. I saw Rui aswell he killed our parents Rui looked at me with wide eyes..

Rui pov:
'I killed Oto-san and Oka-san' I thought I heard footsteps I looked up to see my Onee-san my eyes widened when she was looking scared
She ran up to me and hugged me
"N-nee-san.." I cried in her arms "Shhh Rui it's ok.." I heard her say "B-but I killed them.." I said crying "I'm sure u didn't mean it.." She said

After that Y/n wanted to be a demon aswell because she wanted to be with her brother forever.

But one day something happened that changed Rui's life..

Rui pov:
Me and Nee-san were just having a late night walk when we heard a stick snap
A/n: Rui doesn't have his family in this one shot
I looked at who or what made that sound then I saw a boy with burgundy hair and green checkered haori my eyes widened when I saw a sword on his waist.

Tanjiro pov:
I was walking to the place/village that I was assigned a mission at when I heard footsteps and smelled demons I quickly ran and hid in a bush but I stepped on a stick and it broke it was quite loud and loud enough to be heard by demons the demons both look at me with wide eyes I gripped on my sword Water breathing First form:Water surface slash! I cutted the arms of the Demon girl.

Y/n pov:
I was surprised and scared when the human boy cutted off my arm it quickly regenerated but I didn't know how to use Blood demon art yet so I couldn't do anything the human boy was getting closer and closer he gripped on his sword and...
I turned around hugging Rui
the human boy cut off my head..the world turned upside down..

Rui pov:
Nee-san hugged me while her back was facing the human boy my eyes widened when I saw her head on the ground slowly turning to ash
"Rui..." I heard her said I went closer to her
"Rui u must escape" Nee-san said "N-no! I will not leave you!" I said while crying "But you have to Rui.." She said she gave me one last smile and said "I love you Rui,Sayonara" She said while she turned into ash.

I ran away from the human he was chasing me but I was faster than him for I am a demon I finally lost him I hid behind a tree and cried
'Nee-san is dead..' I thought 'I will Avenge u Nee-san!' I thought

Timeskip to the part in the series when Tanjiro was fighting Rui:
A/n:I don't remember what they said in the series so I'm making my own😤

Rui pov:
It has been years since Nee-san died I still miss her I stopped in my tracks when I saw a boy with burgundy hair and checkered haori
'It's him..' I thought 'he is the one who killed Nee-san' I thought the boy noticed me and his eyes widened he must've remembered me.

Then Rui and Tanjiro fighted (like in the series)
And of course Giyu came in and cutted off Rui's head

Rui pov:
A human with a mismatched haori cane in and cutted off my head I didn't know that he already did until I felt my world turn upside down
I was shocked I started to cry because I was weak and I didn't get to avenge Nee-san.. I started to turned into ash

I open my eyes and it was really bright I saw Oto-san, Oka-san and Onee-san...
I ran up to them and hugged them
"Welcome back Rui..." I heard Nee-san say.