Elementary school student 4th grader, 9 years old.

She is my half-sister
She often comes to my house to ask for help with her homework...
Also she takes the opportunity to play video games and read some manga.
Recently, she has grown a lot and my mind started to fill with indecent thoughts.
"What would it be like to have sex with a 4th grader?"

Before realizing it, I was violently thrusting her tight hole non-stop while she was trying to hold back her moans. She begged me desperately not to cum inside, but I couldn't hear her voice anymore. I was so excited that I ended up filling her up.
I understand, I understand... it was a terrible idea, but I was unable to resist.