My older sister who really wants to satisfy my boyfriend has nominated me as a training table for sex - Nagase Asami

Asami, a shy and unfamiliar with no knowledge of sex, is worried that her boyfriend doesn't seem to be comfortable. His younger brother, who was trying to comfort him, decided to have him observe for his older sister, who had never looked closely at his dick. However, they both got excited and got a handjob, a blowjob, and an ejaculation. From that day on, my younger brother, Mr. Kun, will become a training tool. While thinking that the siblings are not good, Asami goes along with her boyfriend's sake. Meanwhile, his younger brother, wants to have sex with his sister, makes Asami feel good with his hand, and finally crosses the line...