[I know they are from FMA but until I find a better representation of this creature this is the closest image to the description.]
Who knows how old it is or where it came from or how it came to be. It simply is. In it’s endless search for something it goes and seeks and waits for anything with a soul to come near. When it senses a soul nearby it will try to take half of it, then give part of the never ending void that is inside of it. The emptiness. The nothing that will never be filled. Constantly it seeks to fill itself with anything, but nothing remains.
The best memory for it would be when he had his tenth birthday party. It was a big milestone because his parents said that he was now a young man and would be able to do more things that were usually out of bounds. Like trying his first shot of alcohol and practicing driving down the country back roads. He got many gifts he had wanted and loved them all. The best part was that he was surrounded by family and friends. However that was not meant to last. The worst memory is when all of his family and friends were killed right before his very eyes. (Details pending). The shock was so much that he went numb and empty inside. It was at this precise moment when someone moved in from out of nowhere and changed the boy into this creature.
This isn't the only person that this has happened to. One man causes one person's demise, taking away everything they care about, stripping their keystones out from under them, then comes in at the key moment to change their physical make up and traps them in that emptiness for as long as they survive. Then they go out into the world and create a flood of misery and insanity one person at a time.