A scientist creates a device that allows him to travel to other worlds. His first few trips are awe-inspiring, showing him places that seem impossible, incredible. He might stay longer in each, but the device has a... quirk: it cannot be turned off, indeed, attempting to do so would catastrophically collapse whatever world the user were inhabiting at the time. Further, the device automatically activates once it charges sufficiently, and is keyed to the scientist's biometrics, forcing our scientist into each new world.
At first this doesn't seem too bad: our scientist's work predicts an infinite number of worlds, so he could presumably keep going for the rest of his life. What will happen once he dies is something that he dares not think further on.
But another problem rears its head.
With each new world, he seems to see in the night sky fewer stars. Of course, the inhabitants of each world don't see anything out of the ordinary: things are as they have always been for those that live there. Eventually he finds himself near enough to a researcher in astronomy to get a meeting before his next departure, and learns that, in this world, the estimated size of the universe is far, far smaller than in ours. Our scientist makes a leap of logic, and realises the reason for the diminishing stars: each world is smaller than the last. Over the next few worlds, he gathers more data, performs the relevant calculations, and finds a terrible truth: in only five more jumps the world will be only the size of the solar system. On the sixth, there will be no space for both Sun and Earth...
The Shining Force