Ultra Space, Pokémon Wiki

Ultra Space is a network of several different dimensions accessible though a dangerous portal, the Ultra Wormhole. It is the home of the Ultra Beasts, some other people and Pokémon; each species of inhabitant of Ultra Space has its own dimension to live. Ultra Space is an interdimensional spatial realm filled with crystalline meteoroids and populated by Necrozma and multiple instances of members of the Cosmog line. It links to a number of different universes and dimensions through Ultra Wormhole

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