I'm super kind and weak-willed, so my sister-in-law is always considerate towards me. So I thought it would be okay to do something a little perverted? And when I tried pinching her nipples… Safe! Maybe this means I can go further!? Every day I evolve my nipple play! At first she had a slightly reluctant expression, but gradually it turned into an erotic face of pleasure! At this point, it should be fine, right?! So I started messing with more than just her nipples and built a relationship with my sister-in-law where we could have sex! Honestly, the nipple play that I started as a prank unexpectedly became nipple development. Nowadays, if you just lightly touch her nipples, her lower body shakes uncontrollably; she's become incredibly sensitive.
