Kindan ~Kimi wa Boku Dake no Maiden~

Main character falls in love with his sister. He drives away immoral thoughts, but with each day anxiety increases. Eventually he buys an erotic magazine about voyeurs and eavesdroppers and leaves it in sister's room. He manages to shoot a video of his sister masturbating while reading the magazine. As a next move he sends her her masturbation scene picture alongside instructions for her to follow...

[From vndbreview]