In Pokémon Journeys: The Series, Leon is Ash’s opponent in the Masters Eight final.
Leon is the Champion of the Galar region and the number-one-ranked competitor in the World Coronation Series. His undefeated reputation is established early in Pokémon Journeys, where he is presented as one of the strongest trainers in the world.
Ash faces Leon in the Masters Tournament final at Wyndon Stadium. The full battle is a six-on-six match and includes several special battle mechanics, including Dynamax and Gigantamax. Ash ultimately defeats Leon, becoming the World Champion.
Cynthia, Steven Stone, and Diantha are also Champions who compete in the Masters Eight, which is why they are plausible alternatives. Cynthia is Ash’s semifinal opponent, while Steven and Diantha appear in other tournament matches. Leon is specifically the final opponent and the reigning World Champion before Ash’s victory.