I noticed my rebellious younger sister was troubled about something. Behind her annoying attitude, she confessed that her first time with her new boyfriend hadn't gone well. She broke down crying, terrified he might dump her because of it. As her older brother, I decided to step in and help. At first, she protested, "Ew, you? No way, that's gross!" But when I insisted it was for her boyfriend's sake, she stubbornly demanded I teach her. She had a cute side beneath that tough exterior—definitely a tsundere type. I wasn't exactly a veteran myself, but I couldn't deny I was curious about her mature body. Training her like this? Two birds with one stone! I'd teach her everything—from kissing techniques to dirty moves, all the way to orgasm—step by step!