In an ancient time, the great Legendary Pokémons, lead by Arceus, creator of the universe decided no longer move in the realm of the non-legendaries.
They settled down on the Moon of Arcasia… a moon created especially for the legendaries. A number of them refused to go and stayed with the normal Pokémons. Though due to their lesser might compared to greater legendaries, Arceus allowed their stay but they were forbidden to meddle with the problems of the normal mons.
Years after the leaving of the great legendaries, a seal was broken… a seal that kept demonic forces which only wanted the blood and souls of others from invading the world.
Despite the forbidden rule, the remaining legendaries allied with the desperate Pokémons to fight off the forces but they all lacked a great leader.
They turned in their desperation to Arceus but… due to his decisions and set laws, he refused to interact directly with the dying world.
But he took so much responsibility that he created one last gift to the world… a crown! A crown that was would be worn by a chosen champion.
This great champion was granted access to the power of Arceus self himself. Forming one last army, the champion and its forces cleaned the world from the demons and sealed the portal between the two worlds once more.
The champion wanted to return the crown, but Arceus closed all connections between the world and the Moon entirely by that time. Knowing that keeping the crown is would be too dangerous, temples were built. One temple would contain the crown, hidden and its location and existance would be forgotten over the time. The other temples would have the keys to the main temple.
Legend says a worthy warrior will come… seeking for the crown in race with a dark force which wants the crown as well.