Partner Promises! (Japanese: サトシとピカチュウ、二人の約束Satoshi and Pikachu, the Promise between Them) is the 20th episode of the Sun & Moon series, and the 959th episode of the Pokémon anime. It first aired in Japan on April 6, 2017, as a one-hour special alongside SM021, and in the United States on July 1, 2017, as part of a three-hour special.
Ash reluctantly tags along with Lana, Lillie, and Mallow at the mall. One store’s owner points him toward Treasure Island, a gorgeous place full of wild Pokémon, and offers to lend him her kayak. Soon, he and Pikachu are on their way!
After a great day of exploring, swimming, and meeting new Pokémon, they discover a Wimpod stuck in some rocks. Ash tries to scale the cliff to rescue it, but just gets all scraped up until Pikachu recruits an Alolan Exeggutor to give him a lift. Wimpod is freed—and Tapu Lele, Akala’s mysterious Island Guardian (who’s been secretly watching them), shows its approval by healing Ash’s scratches!
Ash and his classmates are at the largest shopping mall on Melemele Island doing some shopping. Ash examines what appears to be candy and Rotom explains that it is a Pokémon food called Poké Beans. Ash wonders which one Pikachu would like while Mallow says that Steenee likes the floral patterned Poké Beans. Ash then decides to go for a Pikachu-colored Poké Bean. Lillie says that she wants to look at scarves and bandannas for Snowy which Lana and Mallow agree to help with, though Ash, Sophocles and Kiawe don't appear as excited. Later, the girls emerge from the shop and Sophocles suggests that this wraps things up. However, Mallow says they are not done yet, as they will be heading to Alola Sunrise, a popular shop which sells accessories made out of natural materials such as Heart Scales and Corsola branches. Kiawe makes an excuse to leave and takes off on his Charizard as well as Sophocles, who says he had forgotten to water the flowers. Rotom also suddenly remembers that Alolan Detective Laki is starting soon, and though Ash mentions that it will be recorded, Rotom leaves, saying that a true Laki fan will be watching it. Realizing what is about to happen, Ash starts to make up an excuse to leave but is stopped from leaving by Mallow.
At Alola Sunrise, Ash and Pikachu watch as the three girls along with their Pokémon try out the accessories on offer before heading outside. He spots an island in the distance, and the manager of Alola Sunrise comes over, explaining that the island is Treasure Island, which she visits to get materials for her shop. She also mentions that she gets to see a lot of wild Pokémon which excites Ash. The manager then offers Ash her kayak to help him get to Treasure Island. Lillie, Lana and Mallow then come over having finished their shopping, and Ash explains to them that he will be heading to the island. Ash and Pikachu then set off in the kayak, and Ash enjoys the sea and the sky, making him feel like they're the only ones on the planet. He continues paddling and they soon arrive on the island.
As they run along the beach, Ash and Pikachu spot a group of Crabrawler where two of them are having a boxing match. As they watch, one of the Crabrawler knocks the other out, which Ash and Pikachu find awesome. They head over to the Crabrawler and ask to join them, but the Crabrawler get intimidated by their eagerness and run away. A Cutiefly then flies past them which lands on Pikachu's nose, causing it to sneeze. Back at Professor Kukui's house, Rotom also sneezes which surprises Professor Kukui, and Rotom wonders whether someone is talking about him.
Back on the island, Cutiefly flies off and Ash and Pikachu follow, arriving at a meadow with many Cutiefly, Ribombee, Butterfree and Comfey. One of the Comfey wraps its lei around Ash's neck. They then spot a group of AlolanExeggutor walking by, and Ash and Pikachu decide to follow, mimicking their walk and speech. The Exeggutor then stop by a spring for a drink, and Ash and Pikachu join them, diving in and joining in the fun. After parting ways with the Exeggutor, Ash and Pikachu sit on a log as Ash's clothes dry in the sun. Ash brings out the Poké Beans that he had bought earlier and gives Pikachu a Poké Bean before helping himself to one. Ash notes that it has been quite a while since they had been by themselves, and reflects that they've met so many people and Pokémon in Alola. Ash then reaffirms his goal in becoming a Pokémon Master before falling asleep. Later, they are awoken by a group of Wimpod who have surrounded them. As Ash wonders what they are, one of them bites Ash on the foot as two of them invade his backpack and take the bag of Poké Beans. The Wimpod scurry away but they chase after them, as Pikachu manages to grab their bag of Poké Beans before the Wimpod dive into the water.
On the beach, Ash watches as the sun starts to set and decides they had better hurry back home. However as they set off, they hear an odd sound. Pikachu senses where it is coming from, and they find a Wimpod stuck in a crevasse. Pikachu tries to squeeze through the hole but is too large to fit in. Ash then notices that he could climb a big cliff face and then climb back down into the crevasse to retrieve the Wimpod. Ash tries several times to climb the cliff face, but keeps falling down. Pikachu has an idea and runs off, as Ash falls again, being distracted by Pikachu. Exeggutor then arrives with Pikachu clinging to its neck. Ash climbs on, and the Exeggutor lifts the two up onto the top of the cliff. Ash thanks Exeggutor for the lift before climbing to where the Wimpod is stuck. The Wimpod gets frightened, and tries to run through a gap in the crevasse. Ash realizes that this is how Wimpod had gotten in, but a big rock had blocked its way back out. Ash tries to move the rock but finds it too heavy, and instead has Pikachu to help him out by using Iron Tail. Pikachu then smashes the rock, and Wimpod leaves to join its friends who had been waiting in the ocean. Wimpod comes back to Ash to thank him, before rejoining its friends. Watching the Wimpod leave, Ash and Pikachu notice something in the sky and spot Tapu Lele flying over to them, scattering its glowing scales. Ash watches amazed as it heals the scratches that he had attained whilst rescuing Wimpod. Surprised, he thanks Tapu Lele before heading home.
Back home, Professor Kukui tells Ash that the Pokémon he saw was most likely Tapu Lele and that meeting it is extremely rare. He also mentions that the Pokémon Ash had helped was most likely a Wimpod. Ash asks Rotom to provide him with data on Tapu Lele, and Rotom helps to explain why his scratches had disappeared. Professor Kukui mentions that Tapu Lele is the guardian of Akala Island, which makes Ash want to see it again.