Kamoku na Imouto

The protagonist moves away from home, and spends every day keeping very busy.  He works so much that his studies are beginning to slip, and he spends his free time blowing off some steam with his beloved eroge collection.

One day, the doorbell rings - suddenly, the protagonist's little sister has come to visit! She can't bear to see her beloved brother's room looking such a mess, so she gets to cleaning, and she wipes out his porn collection in one fell swoop.

Unable to masturbate, the protagonist's mind starts to warp, and soon he's got his pervy sights set on taking his sister for himself!