High school student Akiha Shishido’s life is turned upside down when a mysterious brain colony controlled by the AI Leopard appears out of hyperspace. Akiha is forced to search for parts to repair Leopard. Itsuki Kannagi of the Inter-Colony Police begins her undercover investigation into the appearance of Leopard and its connection to Akiha. Eventually, Itsuki joins forces with Akiha to battle the malicious brain colony Nerval who seeks to enslave all of humanity.