Mother-in-law rearing thus I became my son's slave

My father's new partner, Ichika, is almost the same age as me. I suspected that the marriage was for money due to the huge age difference, so I decided to observe her behavior. One night, a month after I started observing, I quietly peeked into the bedroom and saw Ichika masturbating. Incited by my sadistic feelings, I pursued Ichika while my father was away and began training her as an obedient sex slave...