"Fight! Iczer-One" is a three-episode OVA series that blends science fiction, horror, and mecha elements. The story centers on the conflict between the interdimensional warrior Iczer Robo and the malevolent alien force known as Big Gold. Big Gold, led by the sinister Queen Neos Gold, seeks to conquer Earth by merging it with their own dimension, Cthulhu. To achieve this, they unleash monstrous bio-mechanical creatures called Kaiju to wreak havoc on humanity.

Iczer Robo, a powerful mecha piloted by the warrior Iczer-One, is sent to Earth to combat this threat. Iczer-One forms a psychic bond with Nagisa Kano, a young human girl, to enhance her combat abilities. Nagisa initially struggles with fear and reluctance but gradually embraces her role as Iczer-One's partner. Together, they face grotesque enemies and uncover the dark plans of Big Gold, which involve manipulating human emotions and exploiting Earth's vulnerabilities.

The narrative explores themes of courage, sacrifice, and the bond between Iczer-One and Nagisa. Iczer-One is depicted as a stoic and determined warrior, while Nagisa represents the human perspective, grappling with fear and the moral weight of the conflict. The series also introduces Iczer-Two, a secondary warrior who aids in the fight against Big Gold, adding depth to the story's mecha battles and inter-dimensional warfare.

The plot escalates as Big Gold's forces grow more aggressive, culminating in a climactic confrontation between Iczer Robo and the monstrous creations of Queen Neos Gold. The series balances intense action sequences with moments of emotional resonance, particularly in the evolving relationship between Iczer-One and Nagisa. The OVA concludes with a resolution to the immediate threat, though the broader implications of the interdimensional conflict remain open-ended.