>>150257274
Grimm are the creations of the Dark Brother God who have since been abandoned and taken over by Salem.
Silver Eyes are a power created by the Light Brother God for humans to combat Grimm.
Grimm can range from fodder like Beowulfs to city destroying kaiju.
Salem has also been merging Grimm with humans recent (comparative to the past 50 years of the story), with Silver Eyes also being super effective/partially effective depending.
The depending matter is the human attached to the Grimm matter. Cinder doesn't have Silver Eyes and in spite of having true elemental magic is harmed by the Silver Eyes.
The Hound is a case where the human (well specifically a Faunus which are just humans with animal ears/horns) has Silver Eyes. It was able to temporarily weaken it, but was not enough to kill it out right.
There are arguments for Soul Eater Magic and/or the Black Blood to be of the same vein as Grimm.
There are also arguments for Maka's Grigori soul being special in the same vein as the Silver Eyes.