Nii-chan no Kanojo

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When I returned home, my older brother's girlfriend was there.
It's not like I met her or anything, I just know...
because I can hear her in my brother's bedroom.
They aren't talking though...
She's moaning and groaning... that kind of naughty voice.
The bed is creaking and I can here some kind of slapping sound too.
Listening to that voice made my heart race... and I started playing with myself.
If they found out, I bet they'd get mad...
When I went to the toilet, she was just leaving and greeted me.
She's tall, and pretty, and smells really good.
Another day, she came over to our home again.
But today things are different.
You see, my older brother is away on a trip and isn't home.
I guess she didn't know and came over?
When I tell her my brother isn't home, she replies, "I know."
Then why did she come over...?
"Hey, little brother." she calls to me.
"You fapped off to me, didn't you?"