Cobalt is a combat officer of the all-female Cthulhu alien species. Piloting the giant mecha Delos Theta during Earth's invasion, her primary military objective is deploying a massive black pyramid battle station over Tokyo to cause widespread devastation and engage human forces, aiming to draw out the protagonist Iczer-1.

Cobalt shares a confirmed romantic relationship with fellow officer Sepia, including onscreen kissing. This relationship significantly influences later narrative developments.

During battle against Iczer-1 and her synchronization partner Nagisa Kano, Nagisa's rage unleashes a massive energy beam that cripples Cobalt's mecha. Nagisa then personally delivers the final blow, killing Cobalt.

Cobalt's death triggers Sepia's grief and trauma. This emotional breakdown leads Sepia to accept synchronization with the antagonist Iczer-2, seeking vengeance against Iczer-1 and Nagisa.

No official media beyond the original "Fight! Iczer-One" OVA (1985-1987) features Cobalt. The character does not appear in subsequent sequels, related manga, or audio dramas.