The supernatural community have existed since before humans was created.
Vampires, werewolves, warlocks and all other supernatural creatures lived in peace until the humans were created. The humans feared them and their powers, and soon they had exterminated elves, dwarves, griffins, unicorns and all other creatures they could get.
Few purebloods were left, and the half-bloods only created more chaos for them. They all lived in fear of the humans, hiding away. Pretending. Then the saviors came. They protected supernatural beings from the humans. Helped them to keep hidden. Even killed humans if they had to. They too soon lost control, and humans were near extintion. That was what gave them the name demon. And so Jesus Christ was born. He helped the humans to fight back, and soon all demons hid. No one had really seen them since.
Move forwards to the 21st century. Supernatural beings are still in hiding. Humans are still hunting them. They aren't safe, and the demons know that. But will they ever go out of hiding?
(really bad summary but give it a try)