Somewhere in the far future, aliens that can change form invaded our earth. These seemingly harmful creatures have never been seen in their natural state. Hunters of the Vanguard make sure of that. Unfortunately, the Vanguard organization itself is crumbling quickly as the Props push the humans back more and more in their race for colonization. Vanguard Station XXVI (26) of the Arc Colony is one of the last fully functional bases in the Western Hemisphere, the base nearest to Erina Halley. Erina has lived her whole life waiting for her turn to combat these beings, and she's finally about to get her chance to. The thing is, everything isn't always what it seems...