A flat-chested younger sister and a big-breasted older sister. One day, the younger sister realizes that her sister has extremely sensitive nipples. She sneaks into her sister's room while she is secretly playing with her nipples and pounces! With her tongue technique, she makes her sister cum in an instant, turning her into a sensitive nipple slave! From then on, every chance she gets, the younger sister targets her sister's nipples! Laughing as she plays with her sister's nipples, daily nipple development! The sister becomes so sensitive that even a slight stimulus makes her nipple orgasm. But in the end, it's the younger sister's nipples that...
