~~A My Little Pony & Bionicle Crossover~~ Sister worlds coincide with one another, never knowing about each others' existence until that one moment of crisis. Equestria and Mata Nui serve as a perfect example of such a concept.
Princess Luna is Lost within the stars with a space traveler fighting against penguins, religious Avians, Floran cannibals, and even the oppressive Apex government.
Princess Twilight is the first pony to explore unknown space. Things go bad during the initial flight, and she ends up floating over an unknown planet in unknown space. Now she has to survive long enough to find her way home.