My serious little sister suddenly came to me, a virgin, for advice on sex! My sister wanted to practice sex in preparation for her first time, and I was interested in erotic things, so our interests aligned! However, we made a promise not to go all the way, and we ended up inserting it by mistake! What's more, even though it was my sister's first time, she was feeling it so much that I got carried away and thrust hard, and she came over and over again! From that day on, my sister became super greedy for sex, and I had sex with her all the time, making each other cum over and over again, and we had the best physical compatibility!