Bonnie has been looking for someone to care for her big brother, but what will happen when she finds that someone?

Ash and his friends encounter the Mythical Pokémon Volcanion after a blast of steam from the sky, and Ash becomes bonded to it by an unknown force. Volcanion, who hates humans, is forced to bring Ash along as it heads to the Azoth Kingdom. Volcanion is in pursuit of the artificial Mythical Pokémon Magearna, hoping to rescue it from a corrupt minister who has stolen it with the intent of using Magearna's mysterious power to conquer the kingdom of machinery. Ash and Volcanion are forced to work together to rescue Magearna.