The person in the sex friend photo that my senior at my part-time job showed me was my older sister! - My annoying, super straight-laced, super-serious older sister who was always nagging at my slovenly self was probably happy to be fucked by a member of the opposite sex for the first time since she entered college, and she quickly became a slut who could do it! - I was shocked when my senior asked me if I wanted to have a threesome next time! - I decided to participate because I wanted to make my sister go crazy. - On that day, my sister was surprised and tried to run away, but I caught her and had a threesome with her senior.