Fear
The appearance of millions of Devils was a chaotic and frightening event that made many races imagine the worst
It was not every day that a mysterious being, shrouded in darkness, and ruby eyes gleaming with killing intent would appear in the midst of their territory, without a warning. To those races, the Devils appeared just like that. They would never even think that the Devils had been sealed the deepest parts of their planet, long before they had civilized these worlds.
The Devils didn't attack anyone, but they released their desire to kill and eradicate everyone. They shrouded the worlds in darkness mere minutes after they had been unsealed. Their master was not nearby, so the millions of Devils left the respective places they had been sealed.
At first, the habitants of these planets had been shocked and afraid because the Devils began to encircle their worlds, blocking out the sun and stars with the dark energy their bodies exuded naturally.