The Anime Lad
By 2071, Aragami have consumed much of civilization. Their Oracle cells adapt rapidly, which makes conventional weapons ineffective. Humanity's remaining answer is the God Arc, a living weapon built from those same cells, and the fighters trained to wield one. Extinction has been addressed with equipment that shares material with the problem.
Super Eyepatch Fox
Oracle cells spread, consume life, and become the creatures called Aragami. Cities collapse because normal weapons cannot stop them. God Arcs provide the exception: living armaments incorporating the enemy's own cells. Their wielders, the God Eaters, stand between a shrinking human world and an adaptive hunger ordinary force cannot touch.
Gigguku
The world is being eaten by creatures that adapt past every conventional weapon, so humanity builds living weapons out of their own cells. That is a fantastic ugly solution. God Arcs make the defenders look tied to the threat even before a fight begins. The premise has scale, but that biological link is the detail that makes the apocalypse bite.
Father's Basement
Post-apocalyptic hunters facing monsters immune to ordinary weapons is familiar game-shaped material. God Eater finds its sharper idea in the equipment. God Arcs incorporate Oracle cells, making humanity depend on living weapons drawn from the same source as the Aragami. That uneasy resemblance gives the desperate-war premise a visual and conceptual identity beyond ruined cities.