Belzeus is a member of the Warp Monarch council and the true main antagonist of Chouseishin Gransazer. He is the leader of the Warp Monarch's Earth Invasion Force and the one who caused the war in the first place by tricking the members of Warp Monarch into thinking that the humans are descend from the Bosquito race. His real goal is to conquer Earth so he can gain a vital place in conquering the universe.
He first appears to revive Logia and sends him to destroy Crystal Slab in order to prevent anyone from learning the truth. He later sends Luka to (unbeknownst to her) revive the last Bosquito to motivate the Warp Monarch into attacking Earth in full fury.
During the three day cease-fire between the Warp Monarch and Earth, he sends Brighton down to Earth to locate the Communicator under the guise of locating the descendant of the Bosquito. He later appears to Brighton as a hologram to check up on his progress. When Brighton tells him that the Communicator (Ran) has been identified, Belzeus orders him to kill her.
Belzeus later deploys Gorgion to kill Ruby before she can awaken Ran's power. After he succeeds, he arrives on Earth to kill Ran himself. Pisces, Velsou and Tragos all try to stop him, but he defeats them all. However, Ran's power as the Communicator finally manifest and allow her to contact the Warp Monarch's Will, revealing that the humans are not the descendants of the Bosquito and exposing Belzeus' plans. Upon hearing this, the Warp Monarch allows the Gransazers to deal with Belzeus. They then use DaiSazer to destroy Cabyron and the Garban mothership. Belzeus is later captured by Logia and taken to the Warp Monarch to face judgement.