In a parking lot, Kagetora and Ilima have a battle between their two Eevee. Kagetora's Eevee uses Take Down, but Ilima's Eevee dodges it and scores a direct hit with Swift, fainting the other Eevee. Kagetora compliments Ilima before giving him an Eevium Z. Meanwhile, Ash and his classmates are at the Pokémon School, practicing their moves. Professor Kukui referees the match between Ash and Torracat, and Kiawe and Turtonator. Torracat runs towards Turtonator with a Flame Charge, but it responds with Dragon Tail. Kukui calls for the battle to end, and the two Trainers praise their respective Pokémon's efforts. As Mallow wonders which Pokémon will evolve and grow stronger next, Sophocles asks Ash why Pikachu hasn't evolved yet. Ash replies that Pikachu is fine as he is, and they have made that decision.
Just then, the screams of several girls turns the students' attention to Ilima's unexpected arrival. He runs over to Professor Kukui, who is surprised by the visit. Ilima explains that he arrived in the morning to attend to a few things. Mallow informs Ash that Ilima is a graduate of the school. After class is dismissed, Ash and Lillie learn about the legends of Ilima. Considered to be the best student in the school's history, Ilima skipped multiple grades before flying to the Kalos region for further study. He also has a school-based fan club, which spread rumors that he was responsible for half of Samson Oak's office trophies and that he made Komala's eyes open once.
Meanwhile, Ilima tells Samson and Kukui about his experiences in Kalos. Kukui announces his plans to establish a Pokémon League in the Alola region and invites Ilima to attend it when it is completed; Ilima accepts the offer. Just then, Ash and his classmates arrive and request Ilima to demonstrate his reputation. Ilima is startled at first before being escorted by the students to the bell tower with the hope of seeing Komala's open eyes. Upon hearing Ilima's voice, Komala rolls towards him before returning to its resting place under the bell, much to everyone's disappointment.
Unbeknownst to the group, Zipp peers through a set of binoculars, focusing in on Ilima before driving away. Zipp meets up with Tupp and Rapp, who are talking amongst themselves in an alleyway. Zipp confirms the rumors regarding Ilima's arrival. Tupp accuses Ilima of stealing something from him, and orders Zipp and Rapp to notify the others about Ilima's arrival.
At the school, Ilima is surprised by the out-of-control nature of the rumors. He officially confirms that Komala has always been sleeping, much to Rotom's disappointment. However, Ilima is able to half-confirm the story about him jumping from the large tree. The class, now in swimwear, examine the large tree and nearby lake from the ground. Sophocles explains the concept of a PokéDive; the water sport involves a Trainer and Pokémon jumping and diving together. Lana and Popplio take the first dive. Ash and Pikachu eagerly make their way to a taller jump point. The dive goes great at first, but then, the two lose their form after colliding mid-air and are injured from hitting the water’s surface. Next, Kiawe and his Marowak wave to the crowd below before they attempt a dive. However, Marowak remains on the diving platform shaking because of a fear of water as Kiawe ends up diving solo. The jumps progress onto more acrobatic moves, with Ash and Kiawe imitating Tapu Koko and Buzzwole respectively, and Mallow, Sophocles, Lillie also having a go.
With everyone's encouragement, Ilima agrees to jump. Ilima performs a handstand on the highest diving board before falling into a somersaulting descent with Eevee. The exhibition and well synced display amazes the students. Later, after everyone change clothes back to their normal wear, Sophocles comments that perhaps the dive would have been better if Eevee had evolved into a Vaporeon. Ilima responds that evolution is a way to increase a Pokémon's power, but Eevee already possesses its own abilities. Ilima pulls out his Z-Ring from his back pocket, and the students run towards Ilima to get a better look. The Z-Crystal appears strange to the student. Lillie identifies it as an Eevium-Z and Ilima replies that it was one of the reasons for his visit. Ilima affirms he has no intention of evolving Eevee, and that the Z-Crystal will make it stronger. Ash agrees with Ilima's statement, with striking similarities between their relationships with their Pokémon. Ash explains this is his central motivation for undertaking the island challenges of Alola. Ash, hoping to see Eevee's power, challenges Ilima to a battle. Ilima gladly accepts the request.
Ilima's fans emerge and start cheering for their idol, and in response, Ash's classmates decide to cheer him on. As the match is about to begin several Team Skull grunts ride into the school on their motorcycles. Ilima confronts Tupp and asks that they leave the school's grounds. Tupp criticizes Ilima for not evolving his plain Normal-type Eevee. Tupp brags about how his male Salandit is due to evolve any day now because of its battle experience (seemingly unaware or in denial that male Salandit cannot evolve). Ilima queries who Tupp is, much to his shock. Tupp clarifies, with a flashback to his time as a student that Ilima stole his luck with girls. The trio of girls who were impressed with Tupp for already having a Pokémon, an Alolan Grimer, are quickly distracted by Ilima and his Eevee's cuteness. Tupp, dressed in new shades and jewelry. However, his attempts to catch the girls' attention is squandered by Ilima's appearance, and as Tupp looks in shock, the flashback ends. Mallow calls out Tupp for blaming Ilima for something that isn't his fault, but Tupp shouts at her to be quiet and blames Ilima for being popular with girls. With the revelation, Ilima sincerely apologises. However, Tupp is only further angered by the apology and reveals that many of his fellow grunts share similar sentiments against good-looking guys like Ilima for ruining their luck with girls. Tupp declares that he is going to humiliate Ilima as the grunts call out their Pokémon, including a Spinarak, Golbat, Yungoos, Drowzee, Houndour, Ekans, Alolan Rattata, Scraggy, and Alolan Raticate.
Ash and his friends offer to help Ilima, but he tells them to stay back as the Team Skull grunts are only angry with him. He calls on his Eevee's assistance and uses its Quick Attack to run through the horde of Team Skull Pokémon. Eevee performs Baby-Doll Eyes, causing both the grunts and their Pokémon to become immobilised with hearts in their eyes, followed by Swift attack. The attack hits its mark, leaving only Zipp, Tupp and Rapp standing. The remaining trio call upon their Pokémon, Zubat, Garbodor and Salandit. Eevee manages to dodge Garbodor's Venoshock and Zubat's Wing Attack, though it is hit by Salandit's Flame Burst. Tupp believes that he defeated Eevee, but Ilima interrupts the trio's early celebration, and Eevee jumps back up. Ilima explains that despite the plain nature of the Normal type, its one advantage is its few weaknesses. Despite this, Tupp declares that they'll just do whatever they can to make sure that he doesn't lose.
Ilima commends Team Skull's determination and declares that he will use Eevee's exclusive Z-Move. He forms the Eevium Z pose, calling upon Eevee's friends for assistance. Eevee's cry echoes across Melemele Island, with all of its evolutions running to its aid, and a Vaporeon emerges from the school's water in time. The Pokémon assemble, lending their elemental powers to Eevee, who uses Extreme Evoboost to increase its stat abilities. All of the female Team Skull grunts are immobilized and dazzled by Eevee's cute display. Before Tupp and Zipp can attack, Eevee fires its Last Resort at them. The impact sends the Team Skull grunts blasting off, with the females bidding "Sir Ilima" farewell. Ilima's fans cheer for him and Eevee's evolved forms depart. Ilima tells Ash that they will have a match some other time. Sophocles now understands Ilima's thoughts on unevolved Pokémon and strength.