Sepia, a warrior of the all-female Cthulhu species under Sir Violet’s leadership, commands the alien fortress Nova and spearheads combat operations by piloting advanced mecha units against Earth’s forces. Her fierce loyalty intertwines with a romantic bond to fellow soldier Cobalt, whose death at the hands of Iczer-1 and Nagisa ignites an unrelenting thirst for vengeance.

Tasked by Sir Violet to co-pilot the formidable Iczer Sigma alongside the ruthless clone Iczer-2, Sepia channels her rage into calculated warfare, contrasting Iczer-2’s sadistic tendencies. When Iczer-2 callously murders the child Sayoko mid-battle, Sepia’s resolve fractures, disrupting their synchronization and dooming their mecha. Refusing evacuation, she embraces the cockpit’s flames, yearning to reunite with Cobalt in death.

The manga introduces Sepia as an initial antagonist, her mecha vanquished during the Cthulhu’s first assault. The OVA deepens her tragedy, weaving her grief and love into the narrative’s core. Her story remains confined to these original works, with no documented continuation in later expansions of the series.