Guy cross-dress to frequent school and met father's last wish?
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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