Recently, my little sister has grown into an adult-like body. I accidentally saw her panties and her exposed cleavage, and before I knew it, I was hard! Then she said, "Big brother, did you get excited because of me?" and I couldn't help but retort, "You're getting excited because of me too, aren't you?!" It's true that I, a virgin, got an erection. But my sister seemed to be excited by my erection as well... The ugly argument eventually crossed the line we shouldn't have... We both think of it as just a one-day incestuous affair.
