Princess Diancie of the Diamond Ore Kingdom sets out to protect her homeland from a looming danger. Joined by the Carbink who serve as her attendants, she travels in search of the legendary Pokémon Xerneas, though someone is lying in wait along the route ahead. The fantasy special serves as a prequel to the 17th Pokémon movie, Pokémon XY: Cocoon of Destruction and Diancie.