On a new day in the Kanto region, Satoshi is invited by Professor Yukinari Ookido to attend Professor Sakuragi's lab-opening ceremony in Vermillion City. During the ceremonial speech, Professor Sakuragi receives an alert about a possibly rare Pokémon appearing in Vermillion City's harbor, prompting Satoshi and the other trainers to rush to the area in hopes of finding the mysterious Pokémon. At the harbor, they find Lugia—a Legendary Pokémon—engaged in combat with other trainers. Noticing the other trainers' tactics, Satoshi has his partner, Pikachu, strike Lugia with a Thunderbolt attack. Unfazed, Lugia flees, but not before Satoshi determinedly leaps onto its back. To Satoshi's surprise, he meets another boy, Gou, who has also leapt onto Lugia's back. The two ride on Lugia's back as it takes them on a bizarre adventure across the seas. When it sets the two back on the ground, Satoshi and Gou bid their farewells to Lugia and return to the Sakuragi Institute. Impressed by Gou's findings and Satoshi's insights gathered during their encounter, Sakuragi requests that the duo become his new research partners. And so the duo's journey begins, traveling across multiple regions to meet many new Pokémon—including ones that have the ability to Gigantamax!