Kira is a homunculus - an artifical human used as slave labor by the Republic of Akal. For centuries, homunculi have been used to control Daemons - humanoid metal shells containing bound spirits. Kira is one of the first to be designed for a Class IV Daemon, one of the most powerful weapons in existence. But she doesn't want to be a slave. Jaeke is a aimless graduate of the Imperial Academy, one who regrets signing up for the Daemon Corps - the elite fighting force of the Empire of Eresia and the staunch enemy of the Republic. But once he bonds with his Daemon on his first day, life seems a lot more interesting than he thought. He is ready to fight against the Akali, even if it's just to satisfy his bloodthirsty Daemon. Kira and Jaeke would be enemies in any other situation, but when disaster strikes, the fiercest enemy becomes a necessary evil, perhaps even an ally. Beasts of spirit and steel are what humanity has grown reliant on. What happens when the beasts rebel?