Otoboku: Maidens are Falling for Me(2006)

Otome wa Boku ni Koishiteru

Mizuho can't believe his ears when Grandpa's will is read out. Grandpa's final wish is for Mizuho to attend the same academy as Mizuho's mother. The catch is it's an all-girls school. With the help of friend Mariya however, he gets a makeover good enough to fool everyone at the academy.

(Source: Anime News Network)