In the divided land of Japon, the Kingdom and Empire have waged war for over two decades, deploying biological weapons called Human Tanks on both sides. The conflict grew more complicated when the Fourth Armored Corps broke from the Empire and formed the Daihon'ei Army. Six months after that rebellion, the Empire's Royal Human Tanks have gone on the offensive — and somewhere in the Imperial ranks is a traitor who leaked classified Human Tank intelligence. The assignment falls to the youngest Lieutenant in the Royal Army: find and eliminate the informant.