I've noticed it. My little sister's breasts, which used to be completely flat, have recently started to swell. In the past, I wouldn't have thought anything of seeing my sister naked. But now, I've started seeing her as a woman. Unaware of my feelings, my sister continues to cling to me as usual, so naturally, my cock is fully erect! I think to myself that I'm the worst if my sister finds out... yet every day, I can't help but steal glances at her breasts. Then, it turns out my sister had also noticed the change in my crotch! Just as I was feeling depressed, thinking it was all over, my sister suddenly approached me... and we ended up crossing the line we shouldn't have. We, who were once just brother and sister, have changed into a relationship between a man and a woman, and are now spending every day in a stimulating way that is different from before.
