Fusion. The ultimate bond between Gems. When two Gems combine consciousnesses, they create a new being that combines their appearances, abilities, and personalities.
But what happens to the fusion when its components defuse?
There is a place, existing in 5-3/4 dimensions (25% of the time it exists in five and 75% in six, but nobody can tell when it exists in five or six, so they just go with the fraction), where the fusions reside. If the gem of one of the components, any number, or all, get destroyed, the fusion will remain in this realm, known locally as "Fusionland", indefinitely.
When Gems die, they just go to the Ghostworld, where the souls of every living thing go after death. The Ghostworld exists in 7-1/2 dimensions (50% in seven, 50% in eight, impossible to tell when it exists in what).
But this story is not about ghosts, it's about fusions. And two particular fusions are about to go on a very big adventure.
