Pokémon the Movie: Diancie and the Cocoon of Destruction by Kenji Kitamura

[Viz] Awesome Pokémon adventures inspired by the best-selling Pokémon movies! In the underground Diamond Domain, where many Carbink live, the Mythical Pokémon Diancie serves as Princess. The Heart Diamond that sustains the land is beginning to fall apart, and Diancie is not yet strong enough to create a new one. Can Ash and his friends help Diancie discover its true power and save the Diamond Domain?!