When I was cleaning the bath with my sister-in-law, the shower suddenly went on her and her uniform got soaked! I was fascinated by her body line and underwear that were visible through the water and accidentally got an erection! I did it! While I was panicking, my sister-in-law fidgeted in embarrassment, creating an awkward atmosphere! And when I was at a loss as to what to do, my sister-in-law's Hitomi moistened and she approached me! What! Wait! She reached her hand into my crotch, which made me confused! The unexpected erection was the trigger for a secret that I could never tell my parents about, between me and my sister-in-law.