It happened when I took my son Tooru to visit my best friend Mari's house. The four of us, including Mari's son Kouhei, decided to play a game of Twister. As I was touching my body with Kouhei, I started to feel horny, and before I knew it, I couldn't control my desire. Tooru and Mari seemed to have the same feeling and were excited by each other's bodies. And we developed into a mother-child swap with four of us together. Mari and I were x1, and now that I think about it, maybe we were just frustrated...