The Earth has changed. We don't know yet what happened to humanity, but we know it was eradicated. The new Earth is called Makai - the Demon World. Generations of mythological creatures dwell upon the planet, from which the human being has mysteriously disappeared. One day, a wave of energy hits the Earth. The leaders of the demons realize that a robotic alien race from outer space threatens their existence. The explosion turns earth into a wasteland. Many demons die in the chaos of destruction. It is now up to the remaining demons to fend off the alien invaders, to bring back peace to the demonic race, and perhaps to find out more about the tragic fate of humanity.

Last Armageddon can be described as a post-apocalyptic Final Fantasy. Instead of a party of four light warriors who fight hordes of demons, you have a party of four demons who fight... no, not hordes of light warriors, but mysterious robot-like aliens. The turn-based fights are viewed from third-person perspective and are very similar to the battles of early NES Final Fantasies. The demons can attack, cast offensive and defensive magic, and use special skills. Once they reach a high enough level, they morph into stronger forms with more powerful skills.

Dungeon areas are done in pseudo-3D and are viewed from first-person perspective. The player is able to set and use multiple parties of demons, some of which have unique skills. For example, a flying demon can take the party quicker to some locations, avoiding random encounters.