An unexpected incident involving my cute little sister's panties. I was caught masturbating by accident, and she said, "If you obey me for one day, I won't tell Mom," so I believed her. As a result, I was treated like a slave for the entire day. Forced to strip naked, made to perform humiliating acts, and even had her piss all over my body. Despite the degrading situation, my cock keeps getting hard—depicting the conflicting emotions I experience.