From before, I had a relationship with my son, but that alone wasn't enough for me, so I ended up having a relationship with my best friend Reiko's son as well. Later, I found out that she was the same, and at some point, she had also gotten involved with my son. Moreover, Reiko and I weren't just best friends; we were in a lesbian relationship. One time, our sons found out about this. Then, the four of us developed into an incestuous mother-son swap.
