They are responsible for the annihilation of the ancient human civilization of the past (4 billion years ago) because the organization deemed the civilization's technology at that time a grave threat to universe's stability (more on this later). It is eventually revealed that they destroyed it because the Bosquito was running rampant on it. However, Belzeus reignited the conflict by spreading rumors that the humans existing today were the descendants of the Bosquito, leading the Warp Monarch to return to finish the crusade they began long ago.
The Warp Monarch initially sent down a single Akelon to deal with the Gransazers. The Akelon took up the guise of a deceased physicist named Karin Saeki and attempted to play the Gransazers against each other. However, she was eventually outed as a Warp Monarch agent and killed.
The Warp Monarch then sent the Impactors down to Earth with the mission of hijacking Guntras and flying it into the sun to make it go supernova and destroy the Earth. However, this failed too.
The Warp Monarch then sent down several more aliens with the task of wiping out humanity, but the Gransazers managed to repel all of these attempts.
The Warp Monarch later called a three-day cease fire, which Belzeus and his Garban conspirators used to opportunity to send down Brighton, a Warp Monarch emissary, to locate the Communicator under the guise of finding the human with Bosquito DNA. Brighton discovered that Ran was the Communicator and dispatched Algol to kill her, but he was destroyed by the Gransazers. After the three day cease fire ended, Troius came down and attacked an Earth city but he was destroyed by Guntras and Cloud Dragon.
Around this time another Akelon named Ruby came down to Earth, but with the goal of awakening Ran's power as the Communicator so she could reveal that humanity is not descended from the Bosquito. Recognizing the threat she posed, Belzeus sent Gorgion to assassinate her, having Cabyron attack the city to provide cover. The Gransazers attempted to stop him, but Gorgion ultimately succeeded by activating the explosive device attached to him and blowing up Ruby at the cost of his own life.
Tenma later attempted to fly to the Warp Monarch to negotiate, but his ship was struck down by Cabyron, seemingly killing him. In actually, he was retrieved by Ruby and brought before the Warp Monarch's Will, an entity resembling a glowing blue sphere responsible for governing the Warp Monarch. Tenma attempted to negotiate with him, but was unable to, as Earth's voices couldn't reach him unless Ran's powers as the Communicator were awakened.
Belzeus eventually arrived on Earth to deal with Ran himself, defeating any Gransazers that got in his way. He soon reached Ran but before he could kill her her powers as the Communicator awakened and she was able to commune with the Warp Monarch's Will and reveal that humanity was not descended from the Bosquito. Realizing the truth, the Warp Monarch called off the invasion and Warp Monarch's Will stated that they would attack Belzeus. However, Tenma convinced the Warp Monarch's Will to let the Gransazers deal with Belzeus, stating that the Warp Monarch intervening would be no different than what happened 100,000,000 years ago. But there was a twist: a long-buried tragic truth was ultimately revealed when The said Earth's ancient civilization called reinforcement to Warp Monarch to stop Bosquito wreaking havoc. So contrary to what everyone thought, Warp Monarch back then actually attempted to save earth's hapless civilization which unfortunately did not succeed. But Belzeus revived Bosquito in present day, using that as an excuse to manipulate military force of Warp Monarch as his own army, using that army in a bid to destroy Earthlings and take over Earth as his own.
The Gransazers then summon their ChouSeiShin to form DaiSazer and use that to destroy Cabyron and the Garban mothership. His plans foiled, Belzeus makes one last effort to attack the Gransazers only to be captured by Logia, who brings him onto DaiLogian and takes him to the Warp Monarch Council to face judgment. The supreme commander of Warp Monarch, as a restitution for what Belzeus did to Earth in the organization's name, relinquished all its jurisdiction of Earth and entrusted Earth's security solely to Gransazers.
- Karin Saeki