A Guardian Rematch! (Japanese: 電撃猛特訓！カプ・コケコの再戦！！Intense Electrifying Training! Rematch with Kapu-Kokeko!!) is the 19th episode of the Sun & Moon series, and the 958th episode of the Pokémon anime. It first aired in Japan on March 23, 2017 and in the United States on July 1, 2017, as part of a three-hour special.
Ash really wants to have a rematch against Tapu Koko, but he’s not sure about his strategy. Sophocles, who studies Electric-type Pokémon, offers to help! After some research and training at Sophocles Lab, Ash and Pikachu are ready for battle, and so is Tapu Koko.
The speed training pays off as Pikachu zooms around the battlefield and even lands a couple of impressive hits! But the Island Guardian is still too powerful...for now. As it departs, Ash promises to keep training as hard as he can, and both he and Tapu Koko seem to be looking forward to their next rematch!
At the Pokémon School, Ash and Rockruff are in the middle of a battle against Hiroki and his Mudbray. Mudbray blocks Rockruff's Rock Throw with its Double Kick. His classmates watch from the sidelines as the battle continues and Ash powers up to use Breakneck Blitz. Rockruff hits Mudbray with Breakneck Blitz, knocking it out. Ash and Hiroki shake hands and Hiroki agrees to another battle sometime. Ash tells the others he vows to battle Tapu Koko, so it may know how much stronger he can get. Lillie points out that Tapu Koko is an Electric and Fairy type, so he should come up with a strategy based on that. Sophocles offers his assistance and invites him to come by his house later to see his data which can help with his training.
Sophocles and Ash arrive at his house and go inside where Sophocles introduces his mother to Ash. Sophocles's mother goes to make them something to eat as Ash has a look around. Sophocles's mother brings them some homemade malasada donuts. Ash goes to eat one but it is pipping hot. Ash takes another bite and calls it the best, before giving some of it to Pikachu. Soon, Ash is feeling full having enjoyed them, as Rotom reminds Ash that they came to get data for battling Tapu Koko. They head outside where they meet his father as Sophocles introduces them to him. Sophocles takes him to his own personal laboratory that his dad built just for him. Inside, Ash tries a helmet resembling Togedemaru and presses a device which ends up giving him an electric shock and knocking the helmet off.
Sophocles tells Ash that when he had his battle against Tapu Koko, he had analyzed its Electric Terrain. He had come to the conclusion that Tapu Koko had utilized its AbilityElectric Surge to generate it, powering up Electric-type moves. He explains that this will benefit Pikachu as well, but he will require a different strategy when battling with Rowlet and Rockruff. Ash has trouble understanding any of what Rotom and Sophocles are saying and stops their conversation. Pikachu goes over to a wheel where Togedemaru pushes him onto it and starts walking; Ash notes it to be fun as Sophocles gets an idea and tells him it could be just the training that he needs. Outside, Sophocles shows Ash a bigger wheel which Sophocles says will allow them all to run around, making their training fun as well. Ash calls Rowlet and Rockruff out to take part and they go on the wheel but before they start, Sophocles puts a device on their heads and explains he will use it to collect data.
They start walking and soon increase their speed as Sophocles and Rotom check the data. Rotom sees that it is going up fast as Rockruff, Rowlet and Togedemaru end up falling off. Ash and Pikachu start to go even faster which overloads Sophocles's computer, causing an explosion which is noticed by Tapu Koko. Everyone is shocked as the explosion had destroyed the wheel. Checking his computer, a surprised Sophocles informs Ash a high number has been registered. The next day, Kiawe asks Ash how it went, to which Sophocles says it was a major breakthrough. Pikachu starts to sense something and heads outside the classroom, followed by the others. In the schoolyard, Tapu Koko flies down, leading Kiawe to guess it has come to challenge Ash to a battle. Tapu Koko charges at Rockruff and Rowlet and sends them flying before standing in front of Pikachu; Ash deduces that Tapu Koko only wants to fight Pikachu. A group of students gather and are surprised to see Tapu Koko there as Professor Kukui joins them.
The battle gets started as Rotom starts to record. Tapu Koko activates Electric Surge before dodging Pikachu's attack before being hit on the rebound. Pikachu lands another attack before running around Tapu Koko as Tapu Koko watches Pikachu closely. As Pikachu goes to attack, Tapu Koko strikes Pikachu causing damage but Pikachu is able to get up. The match continues with Tapu Koko hitting Pikachu with Discharge. Ash desperately asks Pikachu to get up which Pikachu manages to do, as Ash's Electrium Z begins to glow. Realizing what it means, he apologizes to Tapu Koko for taking so long and they power up their Z-Move. Gigavolt Havoc hits Tapu Koko, pushing it back, but it recovers quickly. Pikachu launches another attack but is sent flying, crashing through a fence and over a cliff. Ash jumps off the cliff after Pikachu and catches Pikachu mid-fall as Tapu Koko swoops down to save them, much to everyone's relief as Rotom takes a picture of it. Ash thanks Tapu Koko for saving them as it flies off and Ash vows to get stronger and battle Tapu Koko again.