Taking place in the 311th year of the Orbital Calendar, the story follows humanity as they have spread out across countless colonies in space. Akiha Shishidou, a girl from one of these colonies, stumbles upon Leopard: a malevolent Artificial Intelligence system that has infiltrated a nearby colony. Determined to seek justice, Akiha teams up with Itsuki Kannagi, an officer from the Inter-Colony Police, Honoka Kawai, a shy young girl, and Imoko "Imo-chan" Shishidou, a robot.