Long ago before before the grim were ever a threat remnent was a world of amazing and terifing magic. Wizards being able to shape the world; to move mountains, create oceans from nothing and some even being able to control time itself. But even with all of the amazing things that could be done with magic more and more people were useing magic to destroy the world.
Because of this two of the greatest magic users of the time came together. The great witch of wilds, Salem and The endless protector of man and magic, Ozpin. together they decided that all magic was to be sealed away so they started the preparations to do so.
As they cast the spell to end all spells quite literally they stood in a antimagic circle so they could retain their magic after the spell was cast and with only a one mistake made through the 3 week process of casting the spell it was done, all magic was gone or so it was thought the mistake that was made changed where all of the magic went instead of disapering into the void it went to a place called The Soulwell the place all souls came from and because of this people still had magic but in a different form aura they called it.
The witch Salam was not happy with this so she created the grim to destroy all with aura because she saw none of the humans or any of the other races as worthy of it. but Ozpin knowing this retaliated with teaching people to use there auras...