In the depths of Diamond Ore Country resides Princess Diancie, where Carbink Pokémon harmoniously dwell. The country thrives on the Sacred Diamond, a colossal gem only she can craft. Yet, lacking the power to create it spells doom as the current gem nears depletion. Desperate, Diancie joins forces with Ash and Pikachu to locate the legendary Xerneas, bearer of sacred energy. Their quest takes a dark turn when they stumble upon the cocoon of Yveltal, the ominous Destroyer Pokémon from Kalos' history.