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 a boy called Hiroki and his Mudbray. Mudbray blocks Rockruff's attack with its own attack. His classmates watch from the sidelines as the battle continues as 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. Ash wants Tapu Koko to 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' mother goes to make them something to eat as Ash has a look around. He sits a table as Sophocles' mother brings him 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. Sophocles takes him to his own personal laboratory that his dad built it just for him. They go inside and Ash tries a helmet resembling Togedemaru and presses a device which ends up giving him an electric shock which knocks the helmet.
Sophocles tells Ash that when he had his battle against Tapu Koko, he had analyzed its electric field. Tapu Koko utilized its abilityElectric Surge to generate it which allows Electric-types to gain more power. This will benefit Pikachu 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 which Ash notes looks like 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 which will make training fun. 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 this 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' computer, causing an explosion that Tapu Koko sees. Everyone is shocked as the explosion had destroyed the wheel as Ash asks what happened. Checking his computer, Sophocles is surprised to see a high number registered. The next day, Kiawe asks Ash how it went to which Sophocles says it was a major breakthrough. Pikachu starts to sense something outside and heads outside the classroom followed by Togedemaru followed by the other Pokémon. In the schoolyard, Tapu Koko flies down leading Kiawe to guess it has come to challenge Ash to a battle. Tapu Koko charges at them and sends them flying before standing in front of Pikachu which leads Ash to guess 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 as 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 uses 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, apologizes to Tapu Koko for taking so long and they power up as the others look on and use Gigavolt Havoc which hits Tapu Koko who recovers. 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. Everyone runs over to the edge and watch as Tapu Koko flies up having saved Ash and Pikachu from the fall, much to everyone's relief as Rotom takes a picture of it. Ash thanks Tapu Koko for saving them and puts them safely on the ground as Professor Kukui checks that Ash is alright as Tapu Koko flies off as Ash vows to get stronger and battle Tapu Koko again.