You found a unique looking PokéBall on the ground in the grass after awakening from a dream about Fairy-Type Pokémon. It was a Purity Ball. A special kind of PokéBall that had the essence and energy of a Fairy-Type Pokémon flowing within it.

Inside, you found one of the most pure Pokémon. It was a Mew. But not just any Mew… A Baby Mew. The small little Mew must have sought you out.