From the review, "HimeHibi: Princess Days Portable starts off simply. Koi Aizaki is attending a normal high school, when one day she's approached after school by two men in black who simply state that her grandfather needs her. Personally, I was searching for the "run like hell" option, but it didn't come up. Koi's cousin Naohito Hayami appears as well, telling her to go ahead, and she goes with them.
She then finds herself at Tenjou Gakuen, a boys high school where her grandpa is head of the board of directors. He wants to make the school co-ed, but is having trouble getting other board members to agree. So, he's registered Koi at the school to prove them wrong.
At first Koi's hesitant about the whole plan, but it wouldn't be much of a game if she just said "No" and returned to her old school. She decides to win over the people at Tenjou Gakuen and prove the school could be just as successful, if not more successful, if it were made co-ed..."