Pokemon Movie 17: Hakai no Mayu to Diancie

Deep beneath the earth, the Diamond Domain is kept alive by a sacred diamond that is beginning to fail. Its ruler, the Mythical Pokémon Diancie, has not yet mastered the power needed to create a replacement, so she leaves home in search of the Legendary Pokémon Xerneas and the guidance that may save her people.

Diancie's journey brings her together with Ash and his friends, but thieves eager to exploit her diamond-making ability pursue them and accidentally awaken Yveltal from its cocoon. With the Diamond Domain running out of time, Diancie must discover her true strength while Ash's group tries to stop Yveltal's destructive rampage.