When the deities came down from the Heavens Arceus the deity of creation created to Pokemon world over 300,000,000 years ago and with it the Pokemon themselves
It when to last as eventually humans came into being around the same time they appeared on Earth Prime. The humans that where born on this Earth had a far greater resistance to great trauma as many of the Pokemon of the planet where dangerous to humans, this way someone could get struck by Lightning and walk away or fall from a hundred feet and get back up with no broken bones.
eventually during the people and Pokemon learned to work together and help one another to build a better society, seeing that his work was good Arceus fell into a deep sleep to recharge his power.
Time passed on and then 3,000 prior to first contact the King AZ of the Kalos became the earliest person to tamper with the energy of the legendary Pokemon, he used Xerneas power to bring his Floette back to life and Yveltal to end the Kalos war. Seeing as how humans would abuse their incredible power many of the legendary pokemon retreated into hiding, become more myth then legend as such less legendary pokemon came into being as they did not want their children to have their powers abused by humans.
History went on from their the battle of the super ancient pokemon to the splitting of the original dragon into Reshiram, Zekrom and Kyurem, the burning of the Tin Tower, Lugia retreating into the sea and began a breeding population of other Lugia to help defend the seas.
And finally to modern day time when villainous teams such as Team Rocket and Plasma's attempts to conquer the world, while organizations such as team flare and Galactic tried to destroy the world and recreate ti in their image.
And now we are here on April 15, 21X5 where the world of Pokemon came in contact with the Galactic Federation...........
Before reality had a name, before the Multiverse came into being their was a universe called Image.Nation.
Image.Nation was the first Universe to come into being and as such it is responsible from the creation of other alternate realities as long as the original exist their will always dimensions coming into being, for if Image Nation ceased to exist then the production of other universe would stop.
It was the Heavenly Father who created this universe and his council of deities who where charged with creating the different worlds.
A Deity was not a god mind you they could age and die as long they where in the world of mortals who where in the service of the one true god, the God of Humanity who made mankind in his image, but like all living beings they had free agency, the power to choose god or evil.
Such deities included:
Arceus: maker of the pokemon and the deity of creation.
The One who would eventually split into Primus and Unicron the deities of Order and Chaos.
Morpheus: the creator of the Nocturne and the deity of the night and dreams whose symbol was the Moon.
Prometheus: the maker of the Solians and the deity of the Day whose symbol was fire.
Archstar: the Deity of Magic who created all magic.
Draconian: the Deity of dragons and the first female deity who laid the first dragon egg
And many more who disappeared in to myth and legend
Eventually the deities went on the create and populate the universe with their powers of creation, each agreeing not to interfere with the lives of mortals unless absolutely necessary.
Finally God himself created Earth Prime and humankind in his image became to latest sentient species to come into being beginning with Adam and Eve, fascinated by the humans and their power to grow in mind and body some of the deities created humans on their own worlds to assist with their creations, Arceus being among that number.
Eventually millions of years later it would be mankind who would begin to unite the Galaxy under their guidance .....and power