Otome Kishi Ima Sugu Watashi o Dakishimete, or 'A Girl Knight is Suddenly Embracing Me' in English (thanks Sarkkoth!) is one of the sweeter eroge I've seen in a while. For fans of the fetish, there's a trap, but he's straight, and doing a solid for his sister. Take a look at the main page HERE and the OP below.
Kiritani Ayato and his twin sister Saya are living in Germany. Saya always wanted to go to a Japanese school, and just when she gets the opportunity to attend the all-girl school of her dreams, she becomes ill. Deciding to man up for his sister, Kiritani dresses up like her to go to school in her stead so she doesn't miss her chance. He benefits too, he's a good brother, and he surrounded by hot women. Win/win.
The game comes out April 26th. Here's some previews.