Having been sent into a mysterious world by accident when battling Tapu Koko, Ash finds himself in front of the Pokémon School, but this is not the world of the Pokémon School he attends. However, the mysterious trainer Ash has befrieneded continues his fight against the Ultra Beast, Guzzlord, who is responsible for all the destruction in this version of Hau'oli City. Will they be able to stop Guzzlord and to bring peace back to this world?

Ash's old friends Brock & Misty are still in Alola and the group decide to go to Akala Island so Brock can meet the famous Rock-type Island Kahuna, Olivia. Brock is very excited to meet her, leaving Olivia a bit bewildered when they meet, but when she learns that he was a Rock-type Gym Leader, she challenges him to a battle. Who will win?