Boku ga Watashi ni Natta Wake ~Josou Keikaku~

Aoi lost his parents when he was a kid. He has been living with his older sister, Mashiro, since then. But their relationship is somewhat odd. Aoi feels happy to be teased by Mashiro. Mashiro also loves to tease Aoi. One day, Mashiro orders Aoi to transfer to Mashiro's school under the disguise of a girl. Her school is a famous boarding girls' school where rich girls enter. Aoi successfully joins them without knowing Mashiro's intention. But days later, a girl finds that Aoi is actually a boy... [From ErogeShop]