A parallel universe is a hypothetical self-contained reality co-existing with one's own. A specific group of parallel universes are called a "multiverse", although this term can also be used to describe the possible parallel universes that constitute reality.
A world within another world
A universe within another universe
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Parallel Us
FanfictionWhen a lock door takes them to another world and they met their parallel self. A BTS fanfiction rewritten.
