Corruption

From Chapter 13 of Moonlight. www.fanfiction.net/s/9835563/1…

"They said that the Faunus watched the Dust fall from the Moon to the Remnant.
Thus, they were the first to use these pure resources to craft the world to their design.
Cut open chasms, erupt volcanos.
And thus, came the Grimm."

This is a fun drawing of Chapter 13 from Moonlight. So far in the story, we know that Ancient Faunus were the first to come into contact with dust. They were nearly all wiped out, allowing the humans to take over. When the humans arrived, they were surrounded by Grimm. Picking up the Dust that's power had been spread wide and far, it had become safer to use. Tougher and more resistant, Humans used the dust to repel and defeat the Grimm. The woes and dangers of Dust are long forgotten.

 After defeating the Broodmother, her Moon Stones; the purist form of Dust preserved from the early ages, scatter into shardlings at Beacon. As they are assembled piece by piece, the Fauna of the school fall ill; Blake, already suffering a Dust related injury with Adam; her age old, normally fine scar on her arm acts as a conduit to it's power, suffering the worst of the side effects. With little voice to stop the activity due to their small number, Weiss discovers that one of the researchers are in league with the White Fang. Made even more evident by the fact at the dead of night the one in question becomes a Grimm and attacks others of his members, Adam meets Blake at her limit, the Moonstone sapping at her soul.

Adam and Weiss join forces in order to stop Blake from drawing blood.

"A Grimm lacks a soul. A Faunus can only fully become a Grimm if they slay another living being."