Otome wa Boku ni Koishiteru

Everything About Fiction You Never Wanted to Know.
Which one is the boy again? Mizuho is the one in the lower right corner.

Mizuho Miyanokouji is a nice guy from a rich family. When he hears that his grandfather left behind a request in his will, he's happy to oblige. Though he becomes a little less enthusiastic when he finds out that that said request is for him to disguise himself as a girl and attend a specific private girls' school. Don't worry, it's all explained later...

Now he has to deal with keeping his gender a secret, helping the girls who admire "her", and learning how to be a better person.

Based on the shoujo-ai visual novel by Caramel Box, although it is more closely related to the Otokonoko Genre than the Yuri Genre.

Compare and contrast Maria Holic. Incidentally, both series have a character called Mariya.

Now has a sequel, Otome wa Boku ni Koishiteru ~Futari no Elder~, Was released on June 30, 2010, which will be receiving an anime version itself.

Tropes used in Otome wa Boku ni Koishiteru include:

Episode 13, the OVA, provides examples of: