My father remarried, and a big-breasted girl named Mitsuki came with her new mother, and I got a step-sister. But she's a bit of a weirdo. She's a nice, quiet girl in front of her parents, but she has no qualms with me, and sometimes she comes to me to borrow money, which is a problem. One day, I got angry and stole my step-sister's panties from the dressing room and was masturbating when she saw me in the act...