It's been years since the wars between humans and Reploids. They now coexist peacefully, with humans using new Biometal technology to give them Reploid-like powers and Reploids giving up their immortality. When a mysterious group attacks a team of couriers delivering Model X and Model Z Biometals, they respond by fusing themselves with the Biometals, creating Model ZX! With powerful abilities at their disposal, they must discover who their enemies are and what they are after.