Ash and his classmates are aboard a ship bound for Manalo Stadium, the venue of the upcoming Manalo Conference. Lillie surprises her friends with an outfit change to represent her more confident self. When the ship docks, Professor Kukui greets his students, informs them that registrations end by the evening, and suggests they tour the island in the meantime. Ash, Kiawe, and Sophocles go to Manalo Stadium, while Lillie, Mallow, and Lana go to the mall to do some shopping.
Meanwhile, Team Rocket sets up their van in preparation for the crowd of spectators. James remarks that their early-release Manalo doughnuts were a success, but Jessie reminds him that they need to be focused on winning the Alola League in order to conquer the Alola region. Meowth remarks that they can get rich while selling doughnuts and still win the League. Jessie suddenly notices a Stufful walk into her line of sight, causing the trio to start searching frantically for its mother, Bewear. However, this Stufful is revealed to belong to a spectator, much to the trio's relief. James admits that they made all preventative measures to avoid Bewear interrupting their plans, namely constructing a relaxing hot spring for Bewear and Stufful to enjoy.
Ash and the boys reach the Manalo Stadium, where they find Hau and Hala. After Hau reveals he is entering the League as well, Kiawe and Sophocles introduce themselves. Ash notices Hau's new Z-Ring, and he explains that he finally cleared his grandfather's grand trial. Hau also reveals that his Dartrix has since evolved into a Decidueye. Ash shakes his backpack to retrieve Rowlet, only to find it asleep. However, Decidueye pecks it into waking up. Rowlet and Decidueye are thrilled to see each other again and exchange a fist-bump. Hau decides to explore the Manalo Stadium with Ash and his friends, with Decidueye and Rowlet flying into the sky.
Meanwhile, as the girls explore the stores, Lana suggests they go for some Pinap Juice. Mallow approaches the counter to order, but she is shocked to see that the attendant is actually her older brother Ulu. He explains that he decided to return to Alola to open a pop-up store, and Mallow replies that she is entering the League. Ulu is thrilled by the news and admits that he'll close up the store to watch her battles.
Team Skull arrives, and Tupp is keen to gatecrash the Manalo Conference, even though Guzma did not order it. When the other Grunts are hesitant, he explains that the plan will enthrall their boss as Guzma dislikes Kukui, and reminds them of Guzma's earlier statement about the League. Rapp asks for more details and Tupp orders the Grunts to just do stuff. Later, Officer Jenny causes Tupp and his teammates to scatter as they are tagging an advertising poster with graffiti. The girls approach Jenny, and she explains that some troublemakers have been littering and picking fights with the visitors. As Officer Jenny leaves to continue her patrol, the girls declare they will intervene if they come across any troublemakers.
Team Rocket's sales are interrupted when a Team Skull Grunt skips the line. Jessie tries to ask the Grunt to rejoin the line, but the Grunt asks irritating questions and kicks over an advertising sign, causing the customers to flee. Two others Grunts soon join him. James then calls out Mareanie to join Meowth and Wobbuffet in a show of force. The Grunts call on their Pokémon, but the trio quickly defeats them. Meanwhile, Gladion and his Lycanroc quickly deal with another Team Skull trio at the docks.
Later, Ash and the boys confront Tupp and his gang during their crime spree and battle their Garbodor, Zubat, and Salandit with Ash's Pikachu and Rowlet, Kiawe's Turtonator, Sophocles's Vikavolt, and Hau's Decidueye. Garbodor uses Sludge Bomb, but Turtonator destroys the incoming attack with Flamethrower. Tupp orders his Salandit to use Scratch, but Rowlet's Seed Bomb knocks him to the ground. Zubat swoops in to use Bite, but Decidueye evades the attack and strikes with Razor Leaf, defeating Zubat. With the battle over, Ash and the others demand to know what the grunts want, and Rapp replies that the League should burn.
Guzma and Plumeria then arrive. Tupp and his gang beg for forgiveness, but Plumeria scolds them for running off and dismisses their attempt to hijack the League as useless. As Guzma prepares to call out a Pokémon, the girls, Hala, and Kukui arrive as well. Kukui confronts Guzma, demanding to know why he is at the League, and Guzma reveals he is following Kukui's advice to enter the League. He then declares he will dominate the arena and ruin Kukui's dreams by ensuring no more Leagues will take place as Champion. He leaves with Plumeria, with Zipp and the others following. Lillie asks Kukui why Guzma is so obsessed with him, but Kukui doesn't respond. Hala proceeds to inform the children that Kukui and Guzma were once his apprentices. However, Guzma was particularly disobedient and had no regard for the traditions of the island challenge. He ran off hoping to prove his strengths without the need for either a Z-Ring or Z-Crystals. Hala admits that he failed to save Guzma's heart, but Kukui feels that the responsibility lies with him. Ash and the others promptly express their determination to win the League and defend Kukui's efforts from Guzma. Kukui thanks everyone for their support.
Overnight, Kukui presents the competitors with a League eve feast. Ash and his friends call out their Pokémon to enjoy the meal. They learn that Gladion, Principal Oak, and Ilima will be participating, while Guzma and Plumeria are also seen in the crowd of competitors. Later, Kukui ushers everyone over for a presentation about the preliminary round rules, presented by the Masked Royal via television screen. He explains that the participants will compete in a free-for-all, where only the final 16 left standing will advance onto the final tournament, a Battle Royal.