High school student. 15 years old.

-"Ugh... last time was too much for me. I'm gonna get something to drink before I pass out; want something?"
-"Ahh... Ah... Onii-chan!... You're such an idiot... Ah...
You didn't have to come five times inside your adorable little sister... Stupid... Ahh.. Get me a Coke."
-"What's that about? Weren't you the one who wanted to do it no matter what? Give me a break!"
-"Onii-chan, you're a complete idiot, haven't you seen the mess you've made? What if you get me pregnant? It's obvious you only think with your dick..."
-"You've got some nerve, coming at me with that?... Let me see..."
-"Ahh... What are you doing, you jerk?! Don't put your fingers in there..."
-"Don't be a brat... You weren't complaining so much when your stupid Onii-chan was nonstop fucking you from behind. Judging by the way you were moaning, it looks like you really enjoyed it."
-"Ah... Ah... I HATE YOU ONII-CHAAAAN!!!... and bring me that Coke... Please..."

Original resolution: https://tokai.fanbox.cc/posts/11273661