Armitage is a woman who shoots first and exists second, and the show trusts you to understand why that matters when everything on Mars wants her erased. The murder mystery collapses into something bigger: a conspiracy to control what gets to be human, and Armitage is caught between being the weapon they made and the person she refuses to stop becoming. Detective Ross gets dragged into her orbit and never escapes it, watching her solve crimes while the government decides whether she deserves to keep living.

In the year 2046, Detective Ross Sylibus is reassigned to Mars, and a country singer traveling on his flight ends up dead. The murdered woman was a Third, an android made to seem fully human in both appearance and touch. Sylibus is teamed with Armitage, an attractive officer with an abrasive manner, and the two look into this killing alongside the murders of several other women on the planet. What they turn up points to a plot that puts both their lives at risk from the Martian government. Across four OVA episodes, the story mixes sci-fi action with mecha, adventure and romance.