The Guardian's Challenge! (Japanese: 守り神カプ・コケコ登場！挑戦、オレたちのZワザ！！The Guardian Deity Kapu-Kokeko Appears! Challenge, Our Z-Move!!) is the second episode of the Sun & Moon series, and the 941st episode of the Pokémon anime. It first aired in Japan on November 17, 2016 as a one-hour special alongside SM001, and in the United Kingdom as a sneak peek preview of the full series on November 20, 2016 as a one-hour special alongside Alola to New Adventure!. It aired in the United States as a sneak peek preview of the full series on December 5, 2016 as part of a marathon with Volcanion and the Mechanical Marvel and Alola to New Adventure!. The final version of the episode was broadcast in the United States on March 17, 2017, and was later broadcast in sequence on May 12, 2017.
Now that Ash has decided to become a Pokémon School student in the Alola region, his classmates throw him a welcome party! Three of them challenge him to various competitions—a balloon-popping contest versus Sophocles and his Togedemaru, a land-and-water race between Pikachu and Lana’s Popplio, and a Tauros race against Kiawe.
Finally, Professor Kukui challenges him to a Pokémon battle, but Tapu Koko interrupts. It wants to battle Ash instead—and it wants him to try out his very first Z-Move, Gigavolt Havoc! As Pikachu unleashes an astonishingly powerful burst of electricity, Ash’s Z-Crystal shatters. He decides to undergo an island challenge trial to earn a new one!
At the Pokémon School, Ash's classmates are playing with their Pokémon. Lana tells her Popplio to make a balloon, which pops, while Sophocles puts Togedemaru in a wheel to charge his computer program. Meanwhile, Lillie walks up to Mallow and recommends to her that she should add some Berries to the Pokémon food in her new recipe. However, as Mallow thanks Lillie for the suggestion, Bounsweet jumps up in front of Lillie, scaring her frozen on the spot. Mallow comments that it is a shame that Lillie is afraid to touch Pokémon, to which Lillie denies. Kiawe walks in, feeling tired after making a delivery to Ula'ula Island. Professor Kukui then enters and greets the class, with Ash and Pikachu behind him. Kiawe notices the new Z-Ring that Ash is wearing. Professor Kukui reveals that Ash will be a student in the Pokémon School and tells the class not to hesitate to help him out with any questions that he has. Ash introduces himself to his new classmates and his intention of becoming a Pokémon Master, saying he is glad to be here.
Soon afterward while Ash is talking to his new classmates, Sophocles and Mallow notice the Z-Crystal on Ash's Z-Ring, with Kiawe identifying it as an Electrium Z. He asks where Ash got it, as he has not taken part in any trial of the island challenge. Ash explains that Tapu Koko had given it to him, which surprises the class. Ash then explains that he had heard Tapu Koko's voice, so he had took off after it, and when he found Tapu Koko, the ring had come floating down to him. Kiawe wonders how Tapu Koko had obtained the Z-Ring, but Ash says it simply felt like Tapu Koko had been telling him the ring was for him. Lillie explains to Ash that she has read about Tapu Koko, and that it is very well known as the guardian who likes to help travelers, but also likes to play tricks and can punish people if it thinks it is necessary. Upon hearing that on rare occasions, Tapu Koko can provide gifts to people, Mallow realizes that Tapu Koko must really like Ash. Sophocles checks with Kiawe who reveals that he got his Z-Crystal from clearing the Akala Island's grand trial. Ash becomes excited that he can now use Z-Moves just like Kiawe, but Kiawe objects strongly, telling Ash about the duties of Z-Move users. Ash says he doesn't understand what Kiawe said, but reassures Kiawe that he will do his best. Professor Kukui tells the class that Samson Oak will be their teacher for the next lesson. Later, Samson Oak, wearing an Exeggutor costume, teaches the class about the different appearances and types of the Pokémon in different regions as Sophocles comments on certain Pokémon's heights being totally different. Oak explains that the reason Exeggutor is different in Alola is because of the local climate. He then says that the AlolanExeggutor they are looking at is a regional variant, and explains the biology of Exeggutor - they are usually Grass/Psychic. This surprises Lillie who mentions that in Alola, Exeggutor are Grass/Dragon. Ash is surprised about the typing of Alolan Exeggutor and runs forward to stroke its tail. Lillie tries to warn Ash about this, but he ends up getting thrown up a ladder before Lillie explains that the tail has a mind of its own.
At Professor Kukui's house, Kukui treats Ash and Pikachu to dinner, where both of them finish their food very quickly. Ash and Pikachu pet Rockruff, and Kukui explains that it has taken a liking to Ash. As Ash continues to pet Rockruff, Kukui receives a phone call from Mallow and agrees to proceed with a welcome party planned for Ash on the following day. The next morning, Ash and Pikachu are late to school, and rushing to make it on time. As they arrive, they are greeted with confetti and Popplio's bubbles, and Mallow explains that they had planned a surprise party for Ash. Sophocles and Togedemaru start by issuing a challenge to Ash and Pikachu, which Ash mistakes for a battle. However, he soon finds out that it is actually a balloon popping challenge. Sophocles uses Togedemaru's spikes to gain the lead, and Lillie tells Ash that he can also use moves to burst the balloons. Ash commands Pikachu to use Thunderbolt, but it is absorbed by Togedemaru's Lightning RodAbility. She then uses Zing Zap to burst the remaining balloons, easily winning the challenge for Sophocles. Lana and Popplio then challenge Ash and Pikachu to a race, unknowingly being watched by a yellow Pokémon from afar. Although off to a strong start, Pikachu starts to fall behind, and Popplio eventually wins the challenge with its superior swimming speed.
Next, Ash is up against Kiawe in a Tauros race, with Kukui and Samson Oak watching them from the balcony. Oak asks the professor if he will take part in the party, to which Kukui replies that he is the fifth surprise. The race ends with Kiawe winning in a photo finish. Kukui walks up to Ash for his surprise, but Mallow says that it is time for lunch first. As they all eat, Ash hears a Pokémon's cry and Tapu Koko appears, much to everyone's surprise. Ash thanks it for bestowing him the Z-Ring, but Tapu Koko grabs Ash's hat and flies around with it. It then flies off towards the forest, with Ash on its heels.
Tapu Koko and Ash race to the forest and everyone else follows behind. In the middle of the forest, Tapu Koko returns Ash his hat, and reveals its will to battle him. Tapu Koko's Electric Surge activates, causing Electric Terrain to come into effect, and it lunges at Pikachu. Pikachu manages to dodge Tapu Koko's Dazzling Gleam and proceeds with Thunderbolt, but this has little effect. Tapu Koko charges at Ash and activates his Z-Ring. Ash realizes Tapu Koko wants him to use a Z-Move. Ash prepares to launch his first Z-Move, as everyone watches nervously. Ash and Pikachu make the required pose and Pikachu fires a strong Gigavolt Havoc, causing a huge explosion. However, Ash's Electrium Z shatters as the explosion settles, and Tapu Koko flies away. Mallow is impressed at how powerful Ash's first Z-Move was, but Kiawe notices that Ash's Z-Crystal had disintegrated. He explains that it was still too early for Ash to fully utilize Z-Moves, as he had not taken a trial. Upon hearing this, Ash decides to participate in the island challenge to prove his worthiness, and his classmates agree that they will be cheering for him.
Back at Kukui's house, Ash receives an Alola Pokédex from Professor Kukui while having dinner, as Ash looks forward to his island challenge.
During the first airing on TV Tokyo as one-hour special, viewers could take part in a three-characters keyword quiz, in which ten viewers could win a Nintendo New 3DS XL Pokémon Solgaleo Lunala Black Edition and copies of Pokémon Sun and Moon. The second character was ワ and the third ザ.
When the Watch Disney XD site and Disney XD app were updated to include episodes from Pokémon: Indigo League on February 11, 2017, the final version of this and the following episode were made available, replacing the special preview previously available through the service.
As the screen flashes between Ash and Pikachu just before Pikachu fires off Gigavolt Havoc, Pikachu can be heard talking but not actually opening his mouth.
When Ash uses Electrobolt on the balloons, Sophocles has a little pile of balloons left to pop, but when Togedemaru is charged up after Pikachu's attack, there's only one layer of balloons left instead of a pile.
The Japanese text depicting Gigavolt Havoc's name when Pikachu is about to use the move is edited out in the dub.
The text saying "To Be Continued" when Ash receives the Rotom Pokédex from Professor Kukui is edited out in the dub.
This only occurred for the sneak preview. For its official debut, the text saying "To Be Continued" was put back in.
In the official debut of this episode's dub, a large portion of the original music is replaced with dub music. However, this was not the case in the preview airing, in which the episode used all of the original music.