The Dark Domain was an extremely vast space at the edge of the Void Vortex, spanning dozens of oblong regions the size of Mycroft's region. Worlds one to eight were spread across within, with many more dead worlds scattered around them.
All worlds were dull and lightless within that region. Since it was unobservable from other regions and their coordinates indeterminable, they virtually did not exist and were hence known as darkness.
But now, the Northern Empire's External Exploration Department was dispatching signals of the strongest frequencies, calling out to the party in World Zero Three amidst that domain that did not exist, ordering them to cease exploration at once, stay where they were and wait for the return teleportation.