"Groizer X" is a science fiction anime series that revolves around the conflict between Earth and an alien race known as the Groizer. The story begins with Dr. Yan, a brilliant scientist who defects from the Groizer forces after realizing the destructive intentions of his own people. He flees to Earth with his daughter, Rita, and a powerful combat robot named Groizer X, which he designed. The Groizer, determined to conquer Earth, pursue Dr. Yan to retrieve the robot and eliminate him.

The protagonist, Jo Kabuto, is a young pilot who becomes the primary operator of Groizer X after Dr. Yan entrusts him with the responsibility of defending Earth. Jo is joined by Rita, who assists in piloting the robot and provides technical expertise. Together, they form the core of the Earth Defense Force, a group dedicated to repelling the Groizer's relentless attacks. The Groizer forces, led by the ruthless Commander Gaira, deploy a variety of advanced weapons and monstrous mecha in their attempts to subjugate humanity.

The narrative unfolds through a series of episodic battles, with Jo and Rita facing increasingly formidable enemies. The Groizer X robot, equipped with advanced weaponry and transformation capabilities, serves as the primary defense against the alien threat. As the conflict escalates, the series explores themes of loyalty, sacrifice, and the moral complexities of war. Dr. Yan's internal struggle with his past and his commitment to protecting Earth add depth to the story, while Rita's evolving relationship with Jo highlights the human element amidst the chaos.

The series maintains a focus on action and strategy, with each episode presenting new challenges and adversaries. The Groizer's tactics grow more sophisticated, forcing Jo and the Earth Defense Force to adapt and innovate. Despite the episodic structure, there is an overarching progression as the characters develop and the stakes of the conflict become increasingly dire. The final episodes culminate in a climactic showdown between Groizer X and the Groizer's ultimate weapon, determining the fate of Earth and its inhabitants.