Up until now, my stepsister had never studied at all. One day she suddenly said, 'I'm going to college!' I was asked by my stepmother to teach her, but... this is impossible! She's way too stupid! I quickly gave up on my idiot stepsister. But then she said that if I taught her how to study, she'd teach me dirty things... I'm a studious type who's good at studying, and my stepsister is a slut who's good at sex... Result... it's a win-win equivalent exchange! So we started secret private lessons!
