After receiving an unexpected call from her younger brother Parker, Chloe reaches her father's laboratory and asks Ash and Goh if they could help. Chloe explains that one of Parker's friends recently got a new Pokémon, which sparked a schoolyard argument over whether it is cute or not. The group arrive at a local park to find several kids bullying Jinny and her Feebas nicknamed Feeby while Parker looks out for his friend. Goh is thrilled to see the Feebas and scans it with his Rotom Phone. Jinny turns to Parker for support, but he feels torn. Ash pipes up, remarking that Feebas is a great Pokémon, and Goh adds that it evolves into something amazing. The other kids refuse to believe the boys, and quickly take a liking to Ash's adorable Pikachu. Raboot then appears, scaring the bullies away. To cheer Jinny up, Ash and Goh invite her to Cerise Park.
At Cerise Park, Feeby starts swimming in the water and befriends Goh's Goldeen and giant Magikarp. Jinny asks the boys what exactly Feebas evolve into. In the lab, Professor Cerise reveals that Feebas evolve into Milotic; said to be the world's most beautiful Pokémon. Parker and Jinny are excited by the prospect, though Ren remarks that making a Feebas evolve takes a lot of effort. Chrysa takes a more optimistic approach, and her research reveals that Slateport City is hosting its annual Friendship Festival. Ash decides he will enter, but Chrysa reveals that only young children like Jinny can participate. Ren adds that it might be a good way to show off Feeby's charm, and Jinny happily cheers that she will enter the festival. Ash and Goh vow to cheer Jinny onto victory. Chloe sighs, feeling apprehensive about Jinny's chances, though her father reminds her that you won’t succeed if you don’t try first.
Jinny returns to Feeby and announces that they will enter the Friendship Festival together, to which Feeby happily splashes around in response. Ash turns to Goh for a training plan, with Chloe reading that the festival is a test of friendship and showing off moves. Ash starts off with a practice battle, ordering Feeby to Tackle Pikachu, but Chloe interjects and shouts that the festival is not a battle. Next, Goh unveils his own plan – to have Jinny and Feebas perform a swimming routine. Jinny suddenly clings tightly onto Chloe before admitting that she cannot swim, stunning everyone. Jinny adds that she really does want to compete and prove everyone wrong about Feeby. The streak of determination incites something within Chloe, and she offers to help Jinny learn to swim. Chloe sets up a small pool for Jinny to practice swimming and orders the boys to strengthen Feeby's chances with a practice obstacle course. Goh has his Goldeen assist, and it elegantly navigates through the course before performing a somersault through a ring at the end. Feeby, however, crashes its way through the obstacles and gets itself trapped in a swimming ring. As the training continues, Jinny is beginning to swim confidently while Feeby has improved as well. Next, they have Jinny and Feeby practice together, which goes well. As Chloe calls it a day, she notices a peculiar but pretty-looking Prism Scale on Feeby. Goh calls to Chloe, saying that he thought she didn’t like Pokémon. She brushes him off, replying that she just wants to cheer on Jinny's determination and hard work. Goh clarifies further, and Chloe now affirms that she wants to see Jinny win.
Later, Jinny and her supporters take a ship and arrive in Slateport City. Goh instantly spots his next target and catches himself a Wingull. Chloe is unimpressed, but Goh reminds her that he aims to catch every Pokémon and reach his dream. Meanwhile, Team Rocket has followed Ash and the others in their Magikarp submarine, and plan to steal the festival Pokémon for themselves.
The Friendship Festival gets underway. Tito and his Corsola get an applause from the crowd before Marin and Seaking take to the stage. Goh is impressed by the others performers, though Chloe, Parker and Ash are quick to remind him that Jinny and Feeby have worked hard. Goh quickly changes the subject, to which Chloe informs him that she had invited Jinny and Parker's other classmates over to her house to watch the event being streamed online. Next, Jinny, with Feeby in her arms, nervously walks onto the stage before leaping into the performance pool. Feeby makes an incredible leap before swimming around Jinny for a whirlpool effect. Jinny and Feeby's performance is going well, even getting compliments from the crowd and her kindergarten friends watching from Vermilion City.
Team Rocket suddenly crashes the festival and performs their motto, destroying the stage set-up in the process. The trio immediately get to work and start stealing the competitors' Pokémon with the grabber claws on their Magikarp submarine. The trio set their sights on Feeby as well, calling on backup from the Rocket Prize Master and receiving a Kingler and Carvanha. Jessie orders Carvanha to use Bite, though Pikachu intervenes with an Iron Tail. Raboot narrowly dodges a Metal Claw from Kingler. As the confrontation rages, Meowth orders Jinny to hand over her Pokémon. Feeby makes an incredible leap to defend its Trainer, but is struck down by Meowth's Fury Swipes. Feeby's oddly colored scale falls off as a result. Jinny tries sticking the scale back on before using her body to defend her flailing Pokémon. The act of kindness triggers evolution, and Feeby emerges as a Milotic. Jessie orders Carvanha to attack with Take Down, but Milotic uses Wrap followed by Water Gun to batter it away. Ash orders a follow up Iron Tail from Pikachu, which sends Kingler crashing into Team Rocket before Feeby sends the villains blasting off with a Twister attack. The nabbed Pokémon are consequently freed and start returning to their Trainers. Jinny and Feeby later receive a special award from the festival organizers for their display of friendship.
Returning to Vermilion City, Jinny and Feeby's hard work and cooperation are praised by the other kindergarteners. Ash, Goh and Chloe, who comments that Pokémon are amazing, watch on as the kids now play together.