故事以位于关东的某所小学为舞台，主要描写以该学校的6年2班中的CP——绫濑花日和高尾优斗、苍井结衣和桧山一翔的学校生活为中心展开的只属于12岁的淡淡的恋情与友情。

Ash, Pikachu, and their friends come to a desert city by the sea. Here they meet the Mythical Pokémon Hoopa, which has the ability to summon things—including people and Pokémon—through its magic rings. After a scary incident, they learn of 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.

In the underground Diamond Domain, where many Carbink live, the Mythical Pokémon Diancie serves as ruler. The Heart Diamond that sustains the land is beginning to fall apart, and Diancie is not yet strong enough to create a new one. While seeking help from the Legendary Pokémon Xerneas, Diancie encounters a group of thieves who want to take control of its diamond-producing power–and who awaken the Legendary Pokémon Yveltal from its cocoon in the process! Can Ash and his friends help Diancie discover its true power, stop Yveltal’s rampage, and save the Diamond Domain?

Ash meets the Mythical Pokémon Volcanion when it crashes down from the sky, creating a cloud of dust—and a mysterious force binds the two of them together! Volcanion despises humans and tries to get away, but it’s forced to drag Ash along as it continues its rescue mission. They arrive in a city of cogs and gears, where a corrupt official has stolen the ultimate invention: the Artificial Pokémon Magearna, created 500 years ago. He plans to use its mysterious power to take control of this mechanical kingdom! Can Ash and Volcanion work together to rescue Magearna? One of the greatest battles in Pokémon history is about to unfold!