The Shadow Mechanics are an unstoppable expanse of ordered darkness.
The Shadow Mechanics are the realm of Vesperius and the home of the Nocten, a mechanically rigid and sadistic kingdom constructed on the inside of the hollow surface of the Moon. An expansive and sordid machine, it works on the principe of large Cog-cities, rotating plates of metal that slide under the hollow surface of the Moon, burning away the Silver Wilderness beneath.
The Nocten fight against the wild chaos of the Wilderness to allow their mechanic society to expand over the remains, using the burning wood as fuel. When they have an advantage, the glow of the forests they've destroyed can no longer be percieved through the crust of the Moon, and from the perspective of the Earth it appears to have gone dark. When the Cog-cities are forced to retreat, however, the Moon waxes once more.