Team Rocket lands at an airport in the Alola region, being on assignment by Giovanni to capture the resident Pokémon. At Professor Kukui's house, he hands the Pokédex to Ash. They head into Kukui's laboratory, where Ash is greeted by a Rotom that is venturing around. After a while, Rotom charges into the Pokédex, activating it. Ash greets Rotom and is surprised when it responds in human language. Professor Kukui requests Rotom to help Ash on his journey. Rotom understands and begins to boot up, telling Ash that it is equipped with an assortment of languages to communicate with people.
Professor Kukui introduces himself and explains that Ash and Pikachu are staying at his place. Ash also introduces his Pikachu to Rotom. Rotom takes pictures of Pikachu and Rockruff and explains that it has a self-learning capability, which Ash does not fully understand. The Pokédex introduces its full name to Ash, which Ash becomes confused with the name. Rotom asks Ash to simply call it Rotom Dex, and Ash tells it to call him by "Ash". Ash asks Rotom Pokédex to provide information on Pikachu, which it does and pulls on Pikachu's tail to test it. This results in Pikachu using Thunderbolt which shocks everyone. In a forest, Bewear is walking about and hears the bushes rustle as a Mimikyu emerges. Bewear looks at Mimikyu before moving on.
Litten passes by the Pokémon School and watches Komala sleeping on a tree before moving on. In the classroom, Ash introduces Rotom Pokédex to his classmates and they introduce themselves. Lillie is amazed to see a Pokédex with a Rotom inside, whilst Sophocles wants to dismantle Rotom to examine its programming, which Rotom quickly refuses. When Samson Oak arrives with Professor Kukui, Ash introduces Rotom to the principal of the school. Rotom becomes confused by Samson's greetings. Mallow explains that he is saying hello, and that he likes to use Pokémon puns when talking. Rotom Pokédex soon understands and begins making a few puns of its own. Professor Kukui starts the lesson by saying that it will be about field work, and suggests to Ash that now that he has his Pokédex, he should catch a wild Pokémon, which leaves everyone excited. Professor Kukui says it should be a new challenge for Ash and he will Destiny Bond them to help him out. Rotom starts to describe Destiny Bond's effect and reassures that they could count on it for information on Pokémon. The group heads out into the forest.
In the forest, Team Rocket are exploring and plan to catch the first Pokémon they see, but as they left Gourgeist and Inkay back at the headquarters, it will be up to Meowth and Wobbuffet to battle Pokémon. Looking around the forest, Jessie finds it creepy and that a ghost may appear out of nowhere. Upon finishing her sentence, the grass starts to rustle and a Pokémon jumps out of it. Team Rocket starts to scream until a Mimikyu lands on the ground. They mistake it for Pikachu and becomes scared when its costume falls down slightly, but Meowth spots that it isn't actually a Pikachu. Hearing Mimikyu's laughter, it creeps Meowth and Wobbuffet out. James asks what Mimikyu is saying, but he refuses to translate it as he thinks it is too scary. Jessie says it actually looks kind of cute and decides to catch it, throwing Meowth at it. As Meowth gets closer, he uses Fury Swipes but it has no effect on the Mimikyu. Meowth becomes afraid of what Mimikyu is saying and orders it to take off its Pikachu get-up. Meowth looks under its rag and promptly faints. Meowth finds himself walking in a long tunnel and wonders where he is before spotting a light in the distance. He runs towards it and sees a Gardevoir, Lopunny, and Glaceon which he begins to chase after them, having fallen in love with them, unaware that they are illusions caused by a Gastly, Haunter and Gengar. Meanwhile, Jessie and James are trying to wake Meowth up. In Meowth's trance, the Pokémon all disappear and he starts to fall below. Jessie and James throw buckets of water on Meowth, waking him up. He thanks them for bringing him back and explains what happened. They all look at Mimikyu in anxiety and run away after hearing rustling noises from a nearby bush. Ash and his classmates are walking into the forest, becoming increasingly excited about encountering a Pokémon in the forest.
Team Rocket notices them and their Pokémon and decides to use the opportunity to capture all their Pokémon, along with the Pokémon they will be capturing in the region. The group of students spots Mimikyu, but when Mimikyu sees Pikachu, it makes it unhappy. Lillie recognizes it as being a Mimikyu from a book that she read, but Rotom interrupts her to provide information. Meowth overhears the information about a scholar who looked under a Mimikyu's rag passing away and realizes how lucky he was, as James notices the Pokédex moving by itself. Ash decides to try and catch Mimikyu and has Pikachu use Iron Tail which hits, but Kiawe is surprised that it does no damage. Mimikyu strikes back with Play Rough before attacking with Shadow Claw. Seeing how strong Mimikyu is, Ash orders an Electro Ball. Mimikyu reflects the attack back to Pikachu with its tail, although Pikachu manages to dodge it. Jessie is impressed by Mimikyu's strength and decides to catch it, much to Meowth's horror. As Ash prepares to order Pikachu to attack, Team Rocket reveal themselves and recite their motto, which Rotom Pokédex takes their organization's name literally. Rotom becomes surprised to see a talking Meowth and starts taking pictures of him. None of Ash's classmates have heard of Team Rocket, but Ash explains that they are bad guys who steal Pokémon. Team Rocket exclaims that they did not know why Ash is in Alola, but they intend to take all of their Pokémon along with Mimikyu. With few Pokémon to use, Meowth goes to battle Pikachu with Fury Swipes as Pikachu attacks with Electro Ball. As the Electro Ball is about to hit, it is deflected by Mimikyu's Shadow Ball, saving Meowth from being hit. Jessie realizes that Mimikyu is helping them out, but this isn't the case as Meowth explains that Mimikyu has a deep hatred towards Pikachu. Jessie allows Mimikyu to attack and it begins to launch another Shadow Ball. Jessie and James are ecstatic about what is going on, however, the Bewear appears behind Jessie and James and carries them away. Rotom Pokédex informs Ash of what Bewear is, and Ash remembers encountering it before. Meowth tells Mimikyu to stop Bewear and help save Jessie and James, which Mimikyu reluctantly does, and they chase after them. Ash is disappointed at not catching Mimikyu, but Lillie says there are lots of Pokémon around. Ash and his classmates set off to find more Pokémon in the forest.