The action takes place in the deep-underground nation of Diamond Ore Country, whose princess is Diancie, where the Pokémon Carbink coexist peacefully. The Sacred Diamond, a massive diamond that can only be made by princess Diancie, serves as the nation's energy supply. The power of the present Sacred Diamond is about to run out, which would mean the death of the nation, but the current princess does not yet have the ability to make such a diamond. In order to obtain the legendary Pokemon Xerneas, which contains sacred power, Diancie joins up with Ash and Pikachu and sets out with them. However, on the route, they discover the cocoon where the Destruction Pokémon, Yveltal, who was thought to have been