Eurtodium. 
It's a rare gem that possesses extreme power, as even the tiniest shard could power an entire city the size of Boston for three years. However, whilst Eurtodium has such great power, it has a terrible consequence as well. 
The power of the Eurtodium can corrupt the soul, causing the victim to go on a rampage, attacking anything in sight. The colors matter, as the violet Eurtodium is the one that causes this. Violet has a demon inside, which whispers and speaks to the possesses, causing them to eventually and slowly turn dark, and twisted. The blue Eurtodium has the soul of a 'good' demon, ones that look towards assisting those and helping them turn away from dark decisions. However, this gem is rare, because they are sought out by Actor and destroyed. 

That is where they come in, Audience and Actor. 
Actor is a demon, much like any other. He has no face, using nothing but masks to show his emotions. His goal is to collect enough Violet Eurtodium to completely possess the human race and, play with them like puppets on a string. 
Audience is the opposing demon, trying to find the Blue Eurtodium to prevent Actor from bringing the world's doom. 

Then, there are the Soulbound. 
Demons, Ghosts, Poltergeists, Banshees- you name them. Creatures, to say the least, are mentally bound to a human host- a human host to aid the others in their attempt to fight for the world. These creatures are often selected due to their abilities, and are tied to a human who often have something to do with the Eurtodium, such as mining. 

Humans are unaware of their demon's presence, whether their intentions are good or bad. They are often just noted as a consciousness, a voice in their head, a side-effect of the Eurtodium. Some listen to the voices, the whispers in their heads, others do not. 

[See OOC for Rules and other information.]