"GR -GIANT ROBO-" is a 10-episode OVA series that blends elements of science fiction, mecha, and political intrigue. Set in a retro-futuristic world, the story revolves around the conflict between the International Police Organization (IPO) and the malevolent organization known as BIG FIRE. The IPO is tasked with maintaining global peace, while BIG FIRE seeks to destabilize the world using advanced technology and powerful weapons, including the titular Giant Robo, a colossal humanoid robot piloted by the young protagonist, Daisaku Kusama.

Daisaku, the son of the late Dr. Kusama, who created Giant Robo, is a skilled and determined pilot. He is supported by a team of elite agents from the IPO, including Taisou, Genya, GinRei, and others, each possessing unique abilities and specialized roles. The series explores their efforts to thwart BIG FIRE's plans, which involve the activation of the Shizuma Drive, a revolutionary energy source with catastrophic potential if misused. The narrative delves into themes of loyalty, sacrifice, and the ethical implications of technological advancement.

The plot intensifies as BIG FIRE's enigmatic leader, Vogler, orchestrates a series of attacks aimed at acquiring the Shizuma Drive's secrets. The IPO faces numerous challenges, including internal betrayals and the moral dilemmas posed by their reliance on Giant Robo, a weapon of immense power. The series builds toward a climactic confrontation, where the true nature of the Shizuma Drive and the legacy of Dr. Kusama are revealed, culminating in a battle that tests the resolve of both Daisaku and his allies.

"GR -GIANT ROBO-" is notable for its intricate storytelling, blending action-packed mecha battles with a layered narrative that explores the consequences of human ambition and the responsibilities of wielding advanced technology. The characters are well-developed, with their personal struggles and relationships adding depth to the overarching conflict. The series maintains a balance between its episodic structure and a cohesive, overarching plot, making it a compelling entry in the mecha genre.