Shadow is a more than a mere absence of light in Golarion. It's a fundamental force, no weaker than the elemental energies, no less vast than the ethereal or astral planes, and far more common in everyday life than any of those esoteric materials. The Shadow Plane is a physical place, a colorless realm that serves as a dark reflection of the Material Plane, and its existence can mold and shape those within it. The fetchlings who dwell there are the descendants of Azlanti refugees, who over generations have been altered by constant exposure to its planar power until they are no longer truly human. Conversely, the wayang found on the Material Plane have been changed by their lack of access to the Shadow Plane, their pathways between their new lands and their original homes destroyed when the sun returned and the Age of Darkness ended.