In this prequel episode, Pikachu's backstory as a Pichu is explained.

Satoshi, Hanako, Barri-chan and Professor Okibo travel to Kuchiba City to attend the opening of Professor Sakuragi's new research lab. The sudden appearance of Lugia causes Satoshi to meet Go, a new Trainer with his own dream, and both of them to go on the ride of a lifetime to learn more about Lugia.

A bunch of Fushigisou are causing chaos throughout Kuchiba City, and Professor Sakuragi sends Satoshi and Go to investigate. While learning the cause of the trouble, they not only learn more about each other but also clash with some old and unwelcome acquaintances of Satoshi's.

Satoshi and Go travel to the Galar Region to investigate reports that Pokemon are growing giant-sized, meeting up with a mischievous Hibanny along the way that seems to connect with Go.

Satoshi and Go continue their investigation in Galar, encountering a Kabigon affected by the mysterious phenomenon, now called "Daimax". Meanwhile, the Hibanny from the previous episode has been following them.

Go and Hibanny have become partners, but Go is still determined to catch Mew someday. However, he finds that catching certain Pokemon isn't as easy as he thinks.

On hearing about the Hoenn Region's Battle Frontier Glass Flute Cup competition, Satoshi immediately signs both himself and Go up. Go's inexperience at battling gets him knocked out in the first round, but Satoshi, Pikachu and Barrierd show him that battling can be fun.

Satoshi and Go meet a Pochama from the Sinnoh region that has run (actually swam) away from its owner Misaki. Traveling to Sinnoh to return it, they learn that Pochama ran away because of its jealousy toward Misaki's Gureggru, who is competing with Pochama for her attention. The two Pokemon decide to settle their quarrel by competing in the Pokémon Drift Ice Race, which Satoshi and Go decide to enter as well.

Reports of sightings of Houou, the Legendary Pokemon Satoshi and Pikachu met long ago, in the Johto region sends Satoshi and Go to Johto in the hope of seeing it. Their journey takes them to an ancient bell tower, where they meet a boy who also wants to see Houou and his grandfather who has lost his belief in the Legendary Pokemon.

Acting on reports about Kairyu, Satoshi and Go begin a search for a mysterious island that may be the Kairyu habitat. To get there, Go catches a Jugon to use as a Ride Pokemon, but its chasing a female Jugon it's fallen in love with sends them headlong into a storm; fortunately, they are rescued by Kairyu who bring them to their island. While learning about the Miniryu, Hakuryu and Kairyu that live there, Satoshi and Pikachu help a Hakuryu who's having trouble learning how to fly.

Poltergeist activity at the research lab is traced to a Gangar, but a race between Satoshi and Go to catch it gets Koharu involved.

Professor Sakuragi give Satoshi and Go tickets to the World Champion League, which is held in Galar's Shoot City. Many surprises await as they reach the Galar region.