Every world has its own key. Once you get that key, you can open a door and transmigrate between worlds.
And to get a key, first you need...
A door.
The boy, a long string of shiny keys hanging around his neck, looked at the unconscious visitor from another world and finally couldn't help throwing his head back and shouting:
"Can this world, full of holes like a sieve, ever get its act together?!"
