Haru no Ashioto The Movie: Ourin Dakkan

One day the else so peaceful mood in the Ourin Gakuen suddenly changes. Kusunoki-sensei, the so-called subheroine, along with most of the students takes over the school after a coup d'état. The principal is beaten and now it`s up to Yuu Sakurano, Yuzuki Kaede and Nagomi Fujikura to take back the school from her and return it to the former peaceful days.

This is the start of a full-scale war, one that this school has never seen before.

(Source: Anime News Network)