Lean, a young Revilian cadet, is thrust into a military clash between his nation and Zafran amid tensions over ancient war machines known as Decimators. Driven by debts owed due to his friend Zean’s family, he enlists as a covert agent under Lieutenant Manning, a tactician with murky ethics. Tasked with infiltrating Zafran’s Decimator excavation sites, Lean encounters Nataruma—a fugitive psychic from Zafran whose lineage intertwines with dimensional rifts—shifting his mission’s trajectory.

Severely injured during operations, Lean loses his sight but gains experimental ocular implants through Captain, a shadowy figure tied to past dimensional disruptions. Forced into uneasy collaboration, Lean and Nataruma transition from adversaries to allies as her psychic prowess compensates for his blindness, allowing him to pilot the Orguss II mecha. Their partnership proves pivotal when Zafran’s King Perion, consumed by a Decimator’s power, unleashes chaos.

As dimensional anomalies escalate, including the resurgence of Decimators and a reawakened dimensional oscillation bomb, Lean infiltrates Perion’s mecha under Manning’s guidance, striking a decisive blow to end the conflict. Captain triggers the bomb to purge extradimensional influences, seemingly erasing Lean, Nataruma, and the Orguss II—though faint traces hint at their survival in splintered realities.

Nataruma’s heritage, rooted in a merged dimension two centuries past, underscores Lean’s entanglement in broader cosmic repercussions. His journey navigates physical adaptation, precarious alliances, and the moral ambiguities of wielding resurrected technology. Confined to the OVA’s narrative, Lean’s origins remain anchored in Revilia-Zafran strife, his evolution shaped by sacrifice, survival, and the unintended legacies of war.