In the Kanto region, Satoshi is invited to Professor Sakuragi's lab-opening ceremony in Vermillion City by Professor Yukinari Ookido. Amidst the event, an alert of a rare Pokémon sighting in the city's harbor interrupts the proceedings. Satoshi and fellow trainers rush to witness Lugia, a Legendary Pokémon, engaging in a fierce battle. Learning from others, Satoshi commands his trusted partner, Pikachu, to strike Lugia with a Thunderbolt attack. Despite their efforts, Lugia escapes, prompting Satoshi to boldly leap onto its back, where he encounters another adventurous boy named Gou. Together, they embark on a thrilling journey with Lugia, soaring through the skies and exploring the wonders of the sea. After bidding farewell to Lugia, Satoshi and Gou are recruited by Professor Sakuragi as his new research partners, setting the stage for an exciting expedition across various regions to discover and befriend an array of Pokémon, some capable of Gigantamaxing!