I forgot the name of this anime can you help?

I'm trying to find an anime that I watched a couple months back it was about a boy who cross dresses as a girl to go to an all girls school because his mom went there and his grandma went there etc. So they want him to go there then he meets a girl who has black hair and she was supposed to graduate from the school already but she couldn't because she had some problems and had to go to the hospital and had to stay there and she missed school. Then I remember in this all girls school they get to announce an Onii-San. That's all I remember please help