My childhood friend and one-year-older sister, Masuzu, is an excellent student. I often went to her house for tutoring. When I told her that I've recently become interested in SM play, she said... let's try it? Awesome! Let's start with a bondage game using cotton rope. It's embarrassing to be fixed in this outfit, and my underwear is already stained… When I teased her with a pen, lewd fluids kept overflowing. I got so excited that I couldn't help but shove my dick into her mouth! Is this what they call fellatio? She looks so miserable! It's unbearable～！It seems like even big sister isn't entirely displeased. Is this masochism awakening? I might have talent… I decided to train her as a masochistic pet.
