Himehibi: Princess Days

Aizaki Koi is attending a normal high school, when one day her grandfather asks her to enroll in his all boys school as an experiment, to convince the board of directors that the school can successfully be turned co-ed.

At first she refuses, but soon she ends up enrolling in this school as the only girl to help her grandfather out.

But there are those who oppose this plan, and soon she begins to receive threatening phone calls from those who wish for her to leave the school...