"AIKa ZERO" is a three-episode OVA series that serves as a prequel to the earlier "AIKa" franchise, exploring the origins of its protagonist, Aika Sumeragi. Set in a futuristic world where much of Earth's landmass has been submerged due to environmental disasters, the story follows Aika as a young recruit in the Blue Fleet, an organization dedicated to salvaging lost treasures from the ocean floor. Aika is assigned to a mission alongside her mentor, Gonzo Kamishiro, and her rival, Karen Minamino, to recover a mysterious artifact known as the "Eden's Bow." This artifact is said to hold immense power, capable of reshaping the world.

The narrative unfolds as Aika and her team face off against the Calbidos Empire, a rogue faction seeking to exploit the Eden's Bow for their own nefarious purposes. The conflict escalates as Aika discovers her own latent abilities and begins to understand the true significance of the artifact. The series delves into themes of loyalty, rivalry, and self-discovery, as Aika navigates her role within the Blue Fleet and her growing sense of responsibility. The dynamic between Aika, Gonzo, and Karen adds depth to the story, with their interactions highlighting both camaraderie and tension.

The plot is driven by a mix of action, intrigue, and character development, with Aika's journey serving as the central focus. Her determination and resourcefulness are tested as she confronts both external threats and internal doubts. The series maintains a balance between high-stakes battles and quieter moments of introspection, providing a well-rounded exploration of its protagonist. By the conclusion, Aika emerges as a more confident and capable individual, setting the stage for her future adventures in the "AIKa" universe. The OVA effectively establishes the foundation for the franchise while offering a self-contained story that stands on its own merits.