Usagi Holic: Roommate wa Dekiai Ookami

Do you have any idea what happens... when a little bunny comes to a den of wolves like this? Hinako has a dreadful fear of boys due to her past. But to save her twin brother Hinata from a crisis, she has no choice but to muster up her courage and attend his all-boys high school in his place! As luck would have it though, Rei, the school troublemaker who also turns out to be her brother's dorm roommate, sees through her ruse on her first day! Prepared to be sent home immediately for her actions, Hinako is surprised when Rei decides to help her out with her plan. And thus, with the single guy who knows her secret by her side, Hinako begins her new, sweet, exciting life as a high school boy! (Source: Manga Plaza)