Her husband's stepchild secretly watched her stepmother take a bath in the middle of the night

During the summer of my third year of college, my mother told me to take a leave of absence because I was absorbed in studying, so I decided to stay at my uncle's house in the countryside for a week. In the countryside, my uncle, the owner of the house, and Rinko, who was very well-groomed, welcomed me, and I felt like I missed the two of them. A few days later, Rinko, who was supposed to be chaste, had a secret meeting with a man at the front door. There's Rinko managing a man with an overwhelming master-slave relationship. When I was stunned by my appearance being 180 degrees different from usual, I was invited to teach a secret that night.