There are magical barriers which exist between various states and realms of existence in the aurbis.
1st - matter | man
2nd - matter | mundus
3rd - man | mundus
4th - man | oblivion (invasion)
5th - man | aetherius (radiation)
6th - mundus | oblivion (invasion)
7th - mundus | aetherius (radiation)
8th - oblivion | aetherius
9th - aurbis | void (wakefulness)
Translation: THE NINTH BARRIER CANNOT EXIST!.
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Note
This head canon was originally developed for Lyithdonea before being used to create the Scrolls of the Nine Barriers mod.