In a desolate era, humanity faces the aftermath of a catastrophic event caused by "shinobi," a noxious material brought on by an asteroid. Seeking shelter from its lethal effects, survivors find solace in "Kairiku," an erstwhile ocean floor. Within the gloom of this environment, a ray of optimism shines with the discovery of the "Holy Weapon Giga Road" and the revered warrior "Yagyuu," who possess the ability to restore equilibrium. Ame, a royal from a collapsed country, must undertake the task of saving the world from impending doom.