The City Inevitable
Sometimes called the Shadowfell or the World of the Dead, the Shadow of a world is the dark reflection of the world where it connects to the Grim Web. As the world ages, it degrades and decays naturally occurring material and transfers the spiritual material that cannot decay into its Shadow for safe storage. Spirits, souls, psychic entities, and mystical forces that are derived from the life-giving energy of the Great Seed can never be broken down, even once shaped. As such, they travel into Shadow.
Once a world ends, anything not extracted from it and taken into Gateheart is flushed from its Shadow into the Grim Web as the connection point is absorbed. From there, the material is funneled into The OSA.