My father remarried, and I started living with his new wife and her daughter. I secretly watched my father and stepmother having sex in the bath, getting excited together with my stepsister. While gripping my erect cock, she whispered, "We're siblings, so you shouldn't get hard," yet stared at me with burning eyes. I discovered her hidden vibrator in her room and secured it inside her panties, bringing her to climax and heightening our arousal. Was this tsundere girl actually a masochist? At this point, maybe incest was inevitable. Even though we weren't blood-related, I decided to give her a creampie anyway.