Prologue:

Of all the Nintendo worlds, possibly the closest together would be the Mushroom Kingdom and Dreamland. In the very distant past, prosperity came from both places. Trade and travel flourished. So much so, that in the distance of both worlds lies an airport between them. With that, Dreamlanders and Mushroom Kingdom folk had homes together, schooled children together, even married together. It was a great era.

However, that era came to an end.
As Dreamland had created the Fountain of Dreams. It's purpose was for the prosperity of all Dreamlanders; to help good dreams come to all the citizens. It was a good setup, until little by little, the Nightmare built up, and infected the dreams of the people. By that time, Mushroom Kingdom immigration halted. Shortly afterwards, the Star Warriors assembled. Thus began the Holy Nightmare wars. Dreamland emerged victorious. Peace returned.
A similar concept in the Mushroom Kingdom arose too. All the races revolted. Following that, a civil war broke out. Dreamlanders, normally peaceful folk, didn't want to have anything to do with this. So slowly, the Dreamlander population diminished. Shortly afterward, the Kingdoms spread apart, like the Mushroom Kingdom, or Beanbean Kingdom. Peace returned, and after generations of fighting, people migrated back into any kingdom they wanted.

But if peace returned to both places, why hasn't travel resurfaced? There are many answers. One is that over the generations, people just forgot; caught up in their own world's affairs. Another one is from the reputation of the two worlds. Dreamlanders caught wind of the Mushroom Kingdom's new trouble; the evil, nasty Koopa King. Too bad they never heard of the hero Mario, whom defeated him many times. On the other hand, somehow Mushroom Kingdom folk were told of Dreamland's troubles with the greedy, selfish, King Dedede. Ironically, they never heard of the exploits of the Star Warrior Kirby who triumphed over Dedede, and is the most awesome Nintendo character ever. And the possibly most obvious one of them all: Nobody cared to go.

But these two still hold a bond: The Star rod. The same found atop the Fountain of Dreams. The very same now found on Rainbow road. Both contain tremendous power, but are only two halves to one whole.