A true hero at heart, Isa Jo takes after his father, Saki Amamiya. He protects the people of Earth from extra-dimensional threats using the Cannon Sword, a weapon usable as both a sword and firearm. However, after being assigned to kill a harmless girl named Kachi, Isa goes rogue to protect her from his former allies. Strangely, Kachi allows Isa to control the latent abilities inherited from his father...