Board Thread:General Discussion/@comment-16841151-20130907034058/@comment-9090085-20130908004503

Storm5573 is referring to the Grim's unknown origins and weapon-like qualities: We know from Pyrrha that both people and animals have light and darkness inside them, but Grim only have darkness, implying they have fundamentally different origins from other "life" in this world. The Deathstalker in ep.7 suggests alot of things about the Creatures of Grim: they are effectively immortal(it's hundreds or thousands of years old, based on the paintings); they don't need to eat, at least in the normal sense(it spent most of that time trapped in cave with nothing to eat); and their sole goal in life is seemingly not have children, but to kill humans(it probably could have broken out of the cave within a few years of being imprisoned, but it didn't even try to leave until a human walked right up to it).

That all suggests that the Creatures of Grim have a purpose: to annihilate humanity; something contrary to natural life, which simply seeks to continue existing.