[HUNTC-270] "No... Why am I making such a naughty face? *Inner voice" I was constantly teasing my super kind and timid sister-in-law, and she suddenly turned into a sensitive girl who made a lewd face and came over and over again. (Censored)

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? So I poked her nipples... and it was fine! Maybe I can do it even better!? I thought, and I improved my nipple play every day! At first, she looked a little reluctant, but gradually her face turned into an erotic 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.