In the ancient times, not long after Arceus created the world. There was a group of smaller deities, who all controlled something in life, such as love, sorrow and conflict. Things went smoothly, and they went with their duties. But things got out of hand when Arceus decided to create humans, and the smaller deities did not like the idea. Despite their disagreement, Arceus continued with his plans, which sent them into a rage, and they rebelled against him, challenging him in a battle for the control over the world.
They were almost a match for him when they fought together, but in the end Arceus fended them of, shredding their powers in the process. And he came to the solution he would rule everything himself, and prepared to kill all of them. But, as he prepared the final blow, one of them said "We will be reborn in your world when the time is right, and we will find a way to regain our powers, and then we shall destroy humans, the curse you placed on our precious creation, and then we shall destroy you!"
And in a single blast, all of them died, and Arceus took their duties, and continued watching his world, not knowing those words were true. As one day, ten thousands of years later, they were reborn, born into the bodies of normal Pokémon, but with their memories and a small part of their powers intact, and a determination to get revenge.
However, Arceus did notice this, and tasked a group of Pokémon to find and kill them, giving them some special powers to counter the shreds of godly power their enemies had. He trusted them, and hoped for their victory, for were the rebel gods to get their powers back, hell on earth would break loose.
