My mother's remarried husband assaulted my sister, which made me see an erection. (Matsumoto Ichika MIAA-272)

My mother's stepfather, who came from her remarriage, used the pretext of disciplining my younger sister to remove her underwear, leaving her completely naked. Although I was standing nearby, I was powerless to help. It wasn't that I lacked courage; rather, I wanted to see my stepfather violate my sister…