My sister suddenly came to my house and said, "Thank you for your hard work! Look at my underwear and feel refreshed!" and showed me her underwear! I couldn't help but look, but I regained my senses! While I was in the bath, she said, "I'll wash your back!" and appeared completely naked! Her developing body made my crotch horny! She rubbed my breasts! My butt was so tight! I couldn't hold it in anymore! I had sex with my sister!