A market that sells unlawful materials to every world among Seven Worlds, apart from the World of Living.
The most popular materials are the ones made using shadow magic, unavailable to the sides of the conflict because of the War.
It is rumored that they have access to Shadow Realm
When there was peace, technology was evolving, and now this evolution is our job.
Materials made from each type of magic - dark, light and shadow. Each side of the conflict is interested in shadow magic and the magic of the opposed side.
They have appeared sometime after everyone realized that the war will never be over.