It has been 50 years since a natural cataclysm unleashed a horde of monsters upon the Earth. In this new world, where effective human weapons do not exist, there are 'first-class pioneers' who can transform themselves into strong warriors using the power of special crystals. Kuroki is a 'second-class pioneer', who surveys the areas where the monsters have been wiped out. Along with his partner Pomukichi, a small dog, he sets out to investigate an area outside Tokyo. But when he gets there, a monster appears...! Kuroki, a non-pioneer, has no countermeasures, until he accidentally discovers a crystal, and is transformed into a giant invincible dragon...?