A kind Kokoro big-breasted sister, unable to bear the sight of her younger brother being dumped by his girlfriend due to premature ejaculation, strips off her clothes and trains him to improve premature ejaculation! She slowly inserts him, then slowly pumps him until he's about to ejaculate with a high-speed hip thrust, stopping just before he's about to ejaculate! But the little brother couldn't bear the plan and ejaculated inside her vagina many times. From that day on, she manages his ejaculation every day to improve his premature ejaculation! Will his premature ejaculation improve if he endures the teasing cowgirl position, which suddenly switches from slow to fast grinding?