Dinosaurs reappear on Earth, stronger and more intelligent than before, led by Dinosaur Satan Gottes, and this time they are trying to rule Earth once more and wipe out humankind. They are alive and even thriving in an underground empire that they have built.

In 1986, Ururu, the leader of the dinosaurs, declares war against humanity. In an attempt to reclaim Earth's surface, some of the dinosaurs evolve into deadly monsters and start wreaking havoc on human population centers around the globe.

The story revolves around the D-Force (D戦隊 D Sentai), and its two members, a brother and sister team of Tachibana Ai (立花 愛) and Tachibana Zen (立花 善), the Special OPs force, whose mission is to combat monsterized dinosaurs and protect humanity. But early in the series, the siblings suffer a near-fatal injury from the massive explosion during the test of a prototype super-tank, predecessor to Izenborg.

In order to keep them alive, they receive cybernetic body parts and other implants, which synchronize with their combat vehicle and form Aizenborg (Ai + Zen + Cyborg; called Gemini in the US version) to fight the dino-army. Halfway through the show their bodies are altered again, and the two are able to combine into a robotic giant that can fight the dinosaurs in close combat. _ prefabricated 3d model_