Imouto-tachi wa Ore no Mono

The protagonist has two younger sisters, Kuon and Aoha. One day, he hears that Kuon has got a boyfriend. He is happy to hear that, but he actually has mixed feelings... However, Kuon breaks up with her boyfriend a while later.

The protagonist thinks, "It's me who've brought up my sisters. I'm the one who can make them happy." His crooked sexual desire finally bursts up and rapes Kuon... His parents find out about it and he is kicked out of his house.

Several years later, Aoha visits his place. He is really happy to see her again, but he thinks about raping her...
"I can't believe a bond of family. What I believe is a sexual connection..." He then decides to make his sisters his sex slaves...