On Melemele Island, a wild Dewpider leaves its nest in search of its own pond to call home. Along the way, it gets caught up in confrontations with various Pokémon who don’t take kindly to intruders.
Dewpider wears a water bubble on its head that lets it breathe on land, so when it sees Lana wearing one of Popplio’s balloons on her head, it thinks she’s a Dewpider, too! The Pokémon School class observes and encourages Dewpider as it searches for a new home, battling opponents in the process. When it finally succeeds, it happily begins building its nest, inspired by its new friend Lana.
At a clear lake in the deep forest, Goldeen, Seaking, Magikarp, and Feebas inhabit the waters alongside Araquanid and its young Dewpider. Araquanid instructs its matured children to leave the nest for other waters. The many Dewpider quickly swim to the surface, with only one lagging behind for a brief rest stop. This Dewpider reaches the surface and produces a water bubble around its head to protect itself from its new environment.
On its quest to find a new home, Dewpider faces several threats, including a Pikipek, which bursts its bubble helmet and forces it to retreat back to the lake. It attempts to leave again, though it is thrown into a tree by a burrowing Alolan Dugtrio. Dewpider startles a climbing Salandit and uses a String Shot against its Fire attack before falling from the tree and bouncing off an Alolan Exeggutor into an inhabited lake. The rival Dewpider unleashes several lashes, sending the other Dewpider to the water's surface. The two engage in a competition to produce the largest bubble and claim the territory, though the rival Dewpider retains its area. External threats continue, including uneven terrain, Grubbin, Alolan Rattata, and a sleeping Pangoro. Once night has fallen, Dewpider finds itself sleeping inside a tree log. Its sleep is disturbed by the bright light from a group of Morelull, and Dewpider decides to follow. Dewpider's curiosity eventually leads it to the ocean.
Dewpider eagerly dives into the sea, swimming around with little hassle before a Sharpedo arrives. All of the lively Corsola and Wishiwashi flee in fear, though Dewpider is unaware of the threat. Dewpider escapes Sharpedo's jaw, leaping from the ocean and onto the shore. The night turns to morning, and Dewpider finds Lana and Popplio playing around. The Water Bubble Pokemon is instantly enchanted when it notices Lana's bubble helmet, with hearts appearing in its eyes. Dewpider's helmet bursts as a result, and the sound causes Ash, Lana, Rotom, Pikachu, Poipole, and Popplio to locate the now-suffocating Pokemon. Rotom correctly identifies the Water Bubble Pokémon, whilst Lana dives into the ocean and saves Dewpider in her arms. Dewpider swims out of Lana's arms before noticing Popplio, whereupon it launched a Bubble Beam attack that Popplio retaliates against. Lana intercepts the brief confrontation, waving Dewpider goodbye and swimming away with Popplio in hand. When Lana reaches the surface and tells Ash that Dewpider is fine, Dewpider emerges from the ocean, instantly clutching onto Lana's pants. As a result, Lana and Ash decide to take Dewpider back to school.
Lana and Ash arrive back on the school grounds, catching up with the rest of the crew. Dewpider remains attached to Lana, and is irritated by the other Pokemon. When Lana pops her bubble helmet, Dewpider escapes and attacks Pikachu and Snowy in the process, since it no longer recognized Lana. Dewpider jumps into the school's lake, but found the water unsuitable after surveying it. Upon seeing Dewpider, Professor Kukui changes the class to an observation lesson focusing on Dewpider, much to everyone else's joy. The Water Bubble Pokémon makes its way through Hau'oli City, avoiding cars and a Spearow. Dewpider finally finds an ideal body of water: a two-tiered pond with lily pads. It launches a Spider Web to mark its new home, much to the anger of a local Surskit. Surskit skates across the water surface before headbutting Dewpider out of it. Professor Kukui explains that Surskit and Dewpider often fight over territory, and Sophocles compares the intense rivalry to that of Zangoose and Seviper. Dewpider's Bubble Beam attack is unfortunately not enough to ward off Surskit's Signal Beam. With Lana's encouragement, Dewpider uses its bubble helmet as a defense against another Signal Beam, deflecting it and hitting Surskit with its own attack. Dewpider launches itself off of the ground, temporarily trapping Surskit in white threads. Surskit manages to break free and then evolves into Masquerain because of the battle's intensity. Pleased with its new wings, Masquerain flies off into the distance, leaving the pond to Dewpider, much to everyone's surprise. The group leaves Dewpider in its new territory as it makes an underwater web network.