Showa 10th. The "Emperor" reigns for many years while recession continues and natural disasters break out. At the same time the Teito Tokyo faction that seeks reforms grows in power.
All all-girl military unit that vowed to protect the emperor hear a rumor that that the ruler is obstructed and can not rule anymore. They decide to organize a coup d'etat to protect the emperor.
That triggered a chain of dreadful events that verged the country in chaos for three months.

[From vndbreview]