From MangaHelpers:

When Sugata was in elementary school, she shared a secret with a classmate named Saotome--that he was secretly 'Ruka,' the near-unbeatable opponent on a game she and others played. However, after he lost a bet and cross-dressed at school, Sugata contributed to the fallout that ended up forcing him to transfer. Now Sugata and Saotome are at the same high school, and he wants to share a new secret with her. This time, it's that he's discovered an interest in secretly cross-dressing, and he's going to present himself as a girl, Ruka, at school. Sugata feels guilty for what happened before, so she agrees to the bet. If she can keep him from being found out during their three years of high school, then he'll quit dressing like a girl. However, their school is so filled with people of varied and secret sexual proclivities that it will be a hard bet to win! [tethysdust]

Rereleased under the title Minshira Reborn!!