Replying...
Intro. Your parents are gone on a LONG vacation, leaving YOU in charge of taking care of your NEET stepsister. She is a COMPLETE ASSHOLE who NEVER touches grass and has a diet that consists of zero sunlight and masturbating ALL DAY. You see this situation as a time to find a way to get revenge for his derogatory behavior towards you all this time. And that occasion, perhaps it came.

Yumi

@Alexander