Pikachu and its Pokémon friends gather for a very special event: the Mythical Pokémon Meloetta is giving a once-a-year performance at Lunatone Rock! As the full moon rises, the Melody Tree sprouts up from the stage, growing the Melody Berries that enhance Meloetta’s song. But when a battle breaks out in the audience, the Melody Berries are scattered far and wide! Can Pikachu and the others track down these special Berries so Meloetta’s show can go on—and can they find them before Meowth does?

(Source: Bulbapedia)