My mother remarried and I had a cute JK sister, but she was dressed in a very defenseless manner, which made my heart pound!! But even though she's my step-sister, I try to suppress my excitement, but whether she knows my feelings or not, my step-sister is at an age where she's too interested in sexual things, and she starts messing with me when my parents are around! And she even plays some risqué sexual pranks on me!! At first I managed to hold myself back, but as her pranks escalated, I finally got a full erection!! Once I got an erection, I couldn't hold myself back and crossed the line...