When you attend a showing of Pokémon the Movie: I Choose You!, you will receive a QR Code that will grant you a Pikachu wearing the hat that Ash wears in the movie—Pikachu (Partner Cap). This QR Code is specific to Pokémon Ultra Sun or Pokémon Ultra Moon and comes with the Pikashunium Z Z-Crystal, allowing Pikachu to unleash its exclusive Z-Move.
Source: The Pokémon Company
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