It's almost time for the finals of the Alola Pokémon League and, on the day before the finals, Ash's mother and Professor Oak arrive all the way from Kanto to cheer him on. However, soon after a group of Meltan appear and start doing something to Ash's Meltan. Gladion, Ash's opponent, is also preparing for the match being supported by his mother Lusamine and sister Lillie. When the match comes to a head the next day, it starts with Ash with the Mythical Pokémon Melmetal versus Ash with the Legendary Pokémon Silvally. Who will win the match?

The Alola League Trophy Ceremony got interrupted by the opening of an Ultra Wormhole and the mysterious Ultra Beast Guzzlord coming through and starts devouring the League venue. Ash, the Island Kahunas, his friends and the Masked Royal all must band together to stop the Ultra Beast from destroying the world. However, this Guzzlord is not the only Ultra Beast comin through the Ultra Wormhole...