Coming home from work one night, I was alone in the bathtub, indulging in masturbation when I suddenly felt someone's gaze from behind. Hurriedly opening the bathroom door, I found my cousin's older sister who was staying over, staring at me while peeking inside, completely naked. She said, "Let's take a bath together," exposing her mature body. As we moved closer and started washing each other, my intense reaction made her visibly pleased. I couldn't help but rub my cock against her large breasts and ass, growing unable to hold back any longer. Smiling, she whispered, "Big sister will teach you proper adult sex," and soon my cock was buried deep inside her pussy as she pleasured me all over.