Minami was living with her boyfriend and the three of them lived together with his younger brother. One day, while her boyfriend was away, her boyfriend's younger brother came to her for advice, saying that he had gotten his first girlfriend, but things weren't going well due to his premature ejaculation. Since she didn't have a boyfriend, she thought, "Oh well," and helped him with all sorts of training to cure his premature ejaculation habit. She grew fond of her younger brother's hard work, and decided to give him some thorough, sticky training while he was away, using Minami's Minami as well...