The Broken Boundary
Our world came to be because of the Celestials and Fiends will be the end of it.
Over 1,000 years ago, Celestials left the world they created for their own safety, fleeing from the demonic fiends that encroached on the world. The boundary that sealed their realm from ours tore, bringing darkness with it. In an attempt to protect their creations, the Celestials used the last of their power to seal the gate once more, but now it fails. The city has colour, the rest has none and the divide between worlds threatens to be broken, forever.