The Rising Volteckers have returned to the Galar Mine in search of a black Rayquaza. During their search, Rico and Roy get separated from Freed, but they hear a mysterious cry and decide to venture deeper. There, they find people and Pokémon who have lost all their energy and vitality! Meanwhile, the Explorers, led by Amegio, have also arrived at the mine in pursuit of Rayquaza...!?

Riko's pendant transformed into a mysterious Pokémon. Seeking its true identity, Riko and her friends head to her grandmother Diana's house, where they finally reunite with her in a hidden ancient castle. Diana recounts Lucius's adventures and the mysterious Pokémon "Terrapagos." Meanwhile, the Explorers, led by Amegio, who had been pursuing Riko and her friends, are approaching the castle…