Diancie, princess of the underground Diamond Kingdom, cannot forge a new Heart Diamond to replace the one keeping her home alive, so she turns to Ash Ketchum and his friends for help finding the Legendary Pokémon Xerneas. Their search leads to the Allearth Forest, where thieves after Diancie's diamond-making power awaken Yveltal from a dormant cocoon. As the freed Pokémon rampages, Diancie must learn to wield her own strength before the Diamond Kingdom collapses. This is the 17th Pokémon feature film, part of the XY series.