My fair-skinned, big-breasted sister-in-law secretly develops her nipples. She develops a predisposition to premature ejaculation, and I have sex with her so that my wife won't find out.

My wife's younger sister, Yuno, came to Tokyo for a summer course and stayed with us for two weeks. She has a heartwarming personality and is indifferent to men's erotic viewpoints, and tends to seduce men without realizing it.Her innocent face and fair skin pierce my romantic heart, so I decided to play with her nipples so that my wife (Yuno's older sister) won't find out. After developing her nipples, she developed a predisposition to premature ejaculation and had sex with her sister-in-law who had sex over and over again.