Prolog: Tell Me A Story.
This story dates back to just after Arceus's creation of the universe. When he has decided that he has created enough legendaries to maintain balance and has turned the creation of new Pokemon to mew. A time when humans didn't have their impressive technology or well developed cities to protect them from the fresh wave of Pokemon. In fact Arceus was worried that the humans were simply going to fall extinct. He couldn't have that. If not for the humans who would bring balance to he himself. Realizing their emanate destruction Arceus decided to not only protect them from natural disasters like meteors and flooding but talked to the humans and made a deal to loan them some his very power in order to bring prosperity for a time.
Under the god's awesome power the humans quickly rose up and built great cities and grew in intelligence almost over night. They quickly learned to use the surrounding Pokemon to their advantage and even learned primitive ways to contain them. It was truly a golden age for the humans.
But then the day came where Arceus decided it was time to reclaim his power from the humans. But the humans had grown attached to the power and did not want to give it up. They plotted to destroy Arceus and keep the power for themselves. They led Arceus into their grandest city and into one of their largest building. There they attempted to murder Arceus.
But Arceus was horribly underestimated and was able to just barely escape. He took back his power and even though he could destroy the humans he stifled his anger. He left but vowed to never again help their kind. Thus marking the end of creation and the last thing Arceus ever made.
This is sad but not the end of the story. Now we shall go forward in time to the near present. Just a few years ago a group of heroes met with Dialga and discovered this betrayal that took place. They borrowed Dialga's power and used it to go back in time in order to warn the humans of what they were going to do. They believed that if they explained things to them that they could get them to willingly give up the god's power.
In the beginning every thing seemed to be going fine. The humans accepted them and heard them out. So the heroes explained everything that was going to happen and told them that it was best to simply follow the gods deal and give him back his power. Thus the Humans and the heroes appeared to became great friends. Then the fated day occurred and the heroes were led to meet with Arceus. But before they knew what was happening they were imprisoned and the humans, using what they learned from the heroes, changed their plans and decided to double their efforts. They had learned every little detail and fixed every mistake they had made. And this time when the god showed up they succeeded in not only stopping him from taking back his power, but killing him so he could never again return for it.
When the heroes learned of these events they escaped and attempted to save Arceus. They fought their way to the last remaining piece of power that He had left, the very power the humans were so determined to keep, and used it to revive the god. The god was furious of his betrayal and would not listen to anyone. He rained destruction down on the humans and sought to destroy them all thinking nothing of his saviors.
In the end the heroes and the humans teamed up and murdered the god a second time. They could not let him be revived again or they feared nothing would stop him from simply unmaking all of existence so they scattered his power among his first creations the so called legendaries who were to keep balance and asked them to guard them so no one would ever be able to revive their god again. The legendaries did not like this idea but decided it was for the best to prevent the return of their own creator if it meant maintaining balance, the one thing he valued over all.
Author's note: If you thought this story sounded a little familiar or interesting please take some time and look up a movie called "Arceus and the Jewel of Life". I almost summed it up perfectly and only added a few MAJOR changes. I cant tell you what those changes are because that would be spoilers, so either you have seen the movie and know what I changed, or you should watch it. I do hope you enjoy the rest of the story which will be probably be more original.