"Giant Robo" is a seven-episode OVA series that blends elements of science fiction, mecha, and retro-futurism. The story is set in a world where humanity has achieved a utopian society through the development of Shizuma Drive technology, a clean energy source. However, this peace is threatened by the malevolent organization Big Fire, which seeks to exploit the technology for destructive purposes. The narrative centers on the Experts of Justice, a group of elite operatives tasked with protecting the world from Big Fire's schemes.

The protagonist, Daisaku Kusama, is a young boy who inherits control of Giant Robo, a massive, powerful robot created by his late father. Daisaku is emotionally conflicted, as his father's death is tied to the creation of the Shizuma Drive, and he struggles with the responsibility of wielding such immense power. Alongside Daisaku, the Experts of Justice include skilled fighters and strategists such as Tetsugyu, a martial artist; Ginrei, a swordswoman; and Alberto, a sharpshooter. Each member brings unique abilities to the team, and their camaraderie is tested as they face increasingly dire threats.

The plot unfolds as Big Fire launches a series of attacks aimed at destabilizing the world and seizing control of the Shizuma Drive. The Experts of Justice confront powerful adversaries, including the enigmatic and tragic Genya, who has a personal connection to Daisaku. As the conflict escalates, the series delves into themes of sacrifice, legacy, and the moral implications of technological advancement. The narrative builds toward a climactic showdown, where Daisaku must confront his own fears and the true nature of Giant Robo's power.

The series is notable for its intricate world-building, blending retro aesthetics with futuristic technology, and its exploration of complex character dynamics. The story balances action-packed mecha battles with emotional depth, creating a compelling narrative that resonates with fans of the genre.