I read this book in high-school from the school library, 7 or 8 years ago. I believe its a series, but was only able to read the first book before I graduated. Its a fantasy novel. Probaby 200 pages. Paper back. It started out with the "Historian" introducing himself. He walks into a "story" (world) to experience it and records the story for history.
The story he walks into a new story where the main theme is that everyone born in this world is born with a stone. Light stones are for creation of some sort they call them the builders. Dark stones are for what they call the destroyers. When they are doing what there stones designate their stone glows. The 2 are split by a wall the builders built long before the story takes place.
On the builder side a new child is born with a destroyer stone. The town wants to exile him but his parents fight and said they will raise him to protect instead of destroy. The child's father is a metal Smith amd builds the child wrist braces and a machine to shoot metal balls at him to practice defense.
The child is bullied to the point to where he leaves and goes to the destroyer side of the wall to be with "his people".