Marina Oki hails from Merasinya, an aquatic world whose inhabitants were driven to near-extinction by environmental collapse. To ensure survival, her people underwent cybernetic conversion, replacing their organic forms with mechanical bodies. This experience as a survivor of planetary disaster shapes her core identity. She serves as first officer aboard the mixed-crew vessel Karyu, commanded by Captain Warrius Zero, supporting his mission to capture the space pirate Captain Harlock amidst the uneasy post-war truce between Earth and machine forces. Her Merasinya heritage includes ties to marine snow, a substance connected to the series' broader lore. Throughout the narrative, Marina develops a professional rapport with Zero that deepens into mutual romantic feelings, culminating in love, marking significant personal growth against their demanding military duties. Her background and position inherently create tensions aboard the Karyu, reflecting the fragile human-machine alliance central to the story.