Akuma No Riddle (悪魔のリドル) Anime Trailer. It will be released on April, 2014. Animadted by Studio Diomedea and directed by Kusakawa Keizou.
Haru Ichinose is a student at a private girls' boarding school, Myōjō Academy, who is being targeted by 12 assassins disguised as students and Tokaku Azuma is a transfer student and an assassin who also initially targets Haru, but develops feeling for her and decides to protect her from the other assassins.
Via: ANN.