When Ash, Pikachu, and their friends arrive at a desert city by the sea, they encounter Mythologic Pokémon Hoopa, who has the ability to summon things-including people and Pokémon-through its magical powerful ring. Not long later that they learn a local historic event that happened around 100 years ago about a mysterious hero who brought down the rampage of a horrifying Pokémon and confined it in his magic bottle. Now, the bottled up terror is in danger of escape custody to cause fearsome again! Can Ash help his new friends here get through the darkness within...or will a terrible secret burst out into a clash of legends?