When Ash, Pikachu, and their friends visit a desert city by the sea, they meet the Mythical Pokémon Hoopa, who has the ability to summon things-including people and Pokémon-through its magic ring. After a scary incident, they learn a story about a brave hero who stopped the rampage of a terrifying Pokémon long ago.

Now, the threat that has been bottled up for years is in danger of breaking loose again! Can Ash help his new friend overcome the darkness within…or will a dangerous secret erupt into a clash of legends?