Guy cross-dress to frequent school and met father's last wish? I am looking for an anime, where a guy with long blonde hair dresses as a girl to frequent an all girls school.

It was his father's last wish, his father or grand father not sure, in order to get his inheritance.

His childhood friend also frequented the same place and helps him cross-dress.

There was some sort of sister system in place and aside from that a big sister thing.

I don't remember the date of this anime but the animation looked like something of 2000ish.

Hopefully some one can help me out.
Well, then it must be Otome wa Boku ni Koishiteru. The boy who cross-dresses to get into the all-girl's school is named Mizuho Miyanokouji.

From Wikipedia:


  Otome wa Boku ni Koishiteru revolves around the main protagonist Mizuho Miyanokouji, a male high school student. After Mizuho's grandfather dies, his will is reviewed, which explains his desire to have his grandson transfer to Seio Girls' Academy, the same one his own mother attended and his ancestors founded. Abiding by the will, Mizuho cross-dresses to attend the school. The headmistress, the deputy head teacher (visual novel only), Mizuho's homeroom teacher Hisako Kajiura and Mariya Mikado initially know his secret; Sion Jujo and Ichiko Takashima also eventually find this out. 


Mizuho's friend Mariya Mikado helps him cross dress:


  Mariya is Mizuho's cousin-german who grew up with him and therefore knows him very well. When it was decided that Mizuho would transfer to the all-girls school she also attends, she took it upon herself to transform him into a beautiful girl by the use of makeup, and she seemed to have a lot of fun dressing him up.


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