My sister-in-law, who had never studied at all, suddenly said one day, "I'm going to college!" At my stepmother's request, I ended up teaching her, but... This is impossible! I can't do it! I quickly gave up on my sister-in-law, who is so stupid. But she said she'd teach me naughty things if I taught her how to study... I'm a bookworm and good at studying, and my sister-in-law is a slut, so she's good at sex... As a result... We reached a win-win equivalent exchange! And so my secret private lessons began!