My sister-in-law is very kind and timid, and she is very considerate towards me. So I thought it would be okay to do something a little naughty, right? I poked her nipples and it was fine! Maybe I can do more!? I thought, and I improved my nipple play every day! At first, she looked a little reluctant, but gradually her face turned into a sexy one that looked like she was enjoying it! At this point, it's OK! I started playing with her nipples and built a relationship where we could even have sex! To be honest, I was surprised that the nipple play that started out as a prank had turned into nipple development! Now, my sister-in-law has become so sensitive that her lower body trembles just from a light touch on her nipples.