ONGP-136 - My Best Friend's Little Sister, Caught in the Act

I ran into my best friend's sister, Rui, at the park. After tagging along to help with groceries and ending up staying the night at their place, I witnessed something I shouldn't have: my friend and Rui engaged in a heated, incestuous session right beside me. As I peeked, I locked eyes with Rui, who was struggling to keep her moans quiet while climaxing. The next day, things take an even more twisted turn.