Devil-Chi

Just another average day at your average high school. Fuyuki Hino is a typical student with an ordinary set of friends...except for Sakijo Yomina. Yomi-chan is unbearably shy and can't talk to boys...or girls, for that matter. Even stranger, Fuyuki vaguely remembers some kind of vow he made to her when they were children. But when he accidentally walks into the girls' locker room, he makes a shocking discovery—Yomi-chan is a devil, wings and all! However, this irregular girl still has regular high school problems, including dealing with bullies and just wanting to be liked by others.

(Source: Mangamo)