The symbol, when placed on the chest, acts as the catalyst to the vessel being unlocked and used for its true purpose.... housing the demon. No matter what the living being may be, so long as it has sentience, branding the symbol near the heart or brain will enact this transformation.

You hear the whisper in your head as you press the metal wiring against your chest, curious as to what compelled you to do so in the first place.

"I am here." It states, clearly, and only heard by you. "Your body is now mine. This vessel belongs to me. You and I are now one."

Even if one attempted to peel off the mark, it was too late, as it sunk deep into the chest, burning it... cauterizing the flesh into a glowing symbol of its own. Body contorts, mouth gapes open... and then, the body spontaneously combusts into flame, creating the being known as the Harbinger of Conflagration.

~~~~~

Halloween-styled art trade with  Jmillart. Needless to say, he agreed to a demon, and he wanted a fire demon of himself. So, boom he is a demon. Congrats, you can now toast marshmallows on your body. They'll probably be the best tasting marshmallows ever! Nothing tastes better than that subtle hint of charred flesh!