Satoshi and Pikachu arrive in Lumiose City, a part of the famous Kalos region, as they continue their quest to capture more Pokémon and strive to become the very best. Meanwhile, genius inventor Citron and his younger sister Eureka are exploring the city when they encounter Satoshi, who promptly challenges them to a battle. Their plans are interrupted by a dangerous situation when Team Rocket, having followed Satoshi into Kalos, causes a Gaburias to go on a rampage through the streets.
Far off in the quiet town of Vaniville, a young girl named Serena goes through her daily Sihorn riding practice under her mother's guidance, as her mother is a professional Sihorn racer. After finishing practice, she watches the events unfolding in Miare City on television and spots a boy she knew from her childhood. The sight of him, having left a deep impression on her, awakens a longing to see him again. So Serena sets off for Miare City, determined to find the boy from her past.
Pokemon XY follows the group as they journey across Kalos, each pursuing their own goals—Satoshi taking on Pokémon gym challenges, Citron learning from Satoshi, and Serena searching for what her true dream might be. Along the way, they make new friends, encounter fresh rivals, and repeatedly foil Team Rocket's plots, all while gradually uncovering some of the secrets behind mega evolution.