A plain sister who grew up in an all-girls school and has had almost no contact with the opposite sex is going to a co-ed university. She doesn't want to embarrass herself on her university debut, so she asked me, her brother, to practice with her. At first, it was just talking or holding hands, but because my sister is careless and shows off her panties, cleavage, or presses her chest against me, I can't help but get an erection! Then, my sister's desire to grow up knows no bounds, and she practices with my dick! I never thought I would feel like a woman towards my sister... but it's rock hard!
