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The Necrotic Death Lords quickly began to create their facility made entirely out of Necromancy. Inside of their Necrotic Souls there were spaces similar to Divine Realms, but they were lands of dead and decay named Nether Realms. Inside of them these powerful Undead grew unique Necrotic Materials for the usage of their techniques and spells. They all utilized thousands of such harvested materials from the interior of their Nether Realms and began to quickly conjure the creation of this new facility.
The powerful facility or well, a Building-like Undead was actually something close to the Netherworld Plane's version of Formations. Because in this mysterious Plane the concept of magic as we know it was not useful, nor there was Divine Energy to make Formations. The people of this world had designed their own unique ways of making formation-like structures, through Necromancy!
Check "The Protagonist's Sister Is Actually the Strongest"!