My sister helped me lose my virginity and then treated me like a sex slave. (Jinguji Nao, DDK-174)

I'm getting on in years and still single, but I have a cute little sister. One day she suddenly confessed her feelings to me, tied me to a chair, and then gave me a wet kiss, a handjob, and took my virginity in a cowgirl position! After that, she put a collar on me and kept me as her sex slave...