Casey Shield, a hacker who invented the Dynamax Simulator, and Henry Sword, a boy who repairs gear for Pokémon, both dream of entering the Galar region's Gym battles. For Casey, it's a chance to reunite with her lost Pokémon. For Henry, it's an opportunity to search for the legendary Rusted Sword and Rusted Shield.

During their confrontation with the two mystery Trainers, Henry and Casey receive assistance from Piers, the Gym Leader of Spikemuth. After discovering that someone they already know is working behind-the-scenes with the two rival Trainers, Henry and Casey head to Rose Tower to discover the truth about their adversaries.

Will the Darkest Day descend upon the Galar region?!