Board Thread:Off Topic/@comment-3965075-20150620202833/@comment-26397825-20150622011845

I always thought that Grimm themselves were actually a manifestation of negative emotions and that's why they're drawn to them. Ancient battle sites, scene of death and despair, all those kinds of place would be perfect breeding grounds for Grimm. And as they age they absorb emotions from around them, which is why they grow stronger and smarter.

And the reason they attack things with souls is because of the positivity of the soul itself. Kind of like a dementor from Harry Potter actually.

But that's a headcannon. I eagerly await the day when we get told exactly where they come from.