Haru no Ashioto The Movie: Ourin Dakkan
Genres: Action, Comedy
Type: OVA, Episodes: 1
Aired: Mar 31, 2006
Studio: Asahi Production
Source: Visual novel
Rating: PG-13 - Teens 13 or older
Synopsis:
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: ANN)