In the year 3990, the immortal Oldna Poseidal rules Pentagona, a war-torn solar system of five planets. Daba Myroad is a survivor of the Yaman Clan, just one of numerous native societies nearly wiped out by the tyrant. Living on the remote planet Koam with his friend Mirao Kyao, Daba possesses L-Gaim, a humanoid mecha known commonly as a "Heavy Metal" and the last known relic of the Yaman Clan. The pair befriend Fanneria Amu, an aspiring actress, and Lilith Fau, the last surviving fairy in Pentagona while on the run from a band of thieves attempting to steal L-Gaim. Daba promises to fulfill the dying wish of one of the thieves hunting him—an honorable act that leads him to the powerful merchant Amandara Kamandara. With their mission in sight, the ragtag group will face powerful adversaries and become entangled in a rebellion against Poseidal's reign.

After years of conflict, humans and monsters have settled their differences and are now at peace. This post-war era led to the foundation of Lindworm—a town which has since become the focal point of racial harmony. As a human doctor specializing in monster biology, Glenn Litbeit runs a small clinic alongside his partner, Saphentite Neikes, who is a half-snake monster known as a lamia. He uses his knowledge to tend to any monsters who seek his aid. Whatever affliction, concern, or injury it may be, he will always be there, ready to help. [Written by MAL Rewrite]

In order to explore the newly discovered planet, Promethe, there are many projects are running all over the world. Here in Japan, under the direction of Dr. Oedo, "Space Carrier Jasdum" and "Planet Robot Dangard A" are being built. Ichimonji Takuma is a candidate for the pilot of Dangard A. His father, Ichimonji Dantetsu, was a famous space pilot. However, Dantetsu went missing after a mysterious accident, and the people blamed him for the accident. In order to clear his name, Takuma is trying to become a space pilot and succeed in the project. Will Takuma become the pilot?

The Oishinbo gang takes time off from the normal culinary wars to get involved with a political dispute about American rice imports. The economic conflict between a pushy US Senator from California and a nationalistic Japanese politician is further complicated by concerns about the cumulative effect of pesticide use in both American and Japanese agriculture.