Riolu accompanied Korrina a long time ago at Route 18, from where they saw the crystal sundial at Anistar City. Both of them were searching for a Mega Stone that would Mega Evolve Riolu. Riolu sensed the Mega Stone was on a cliff, across a river. Since the bridge connecting the two cliffs was broken, Riolu and Korrina took a cart and slided down a slope, then Riolu used Bone Rush to make them fly across the river. They succeeded in the task and Riolu obtained the Lucarionite.
Once Korrina and Lucario (who evolved from Riolu) returned to the Tower of Mastery in Shalour City, Gurkinn approved of all the tasks they completed on their journey and gave Korrina a Key Stone to Mega Evolve Lucario.
Korrina, along with her Lucario, arrived to Santalune City, where they found the group chasing after Celosia, who stole the Mega Ring. Korrina Mega Evolved her Lucario, who used Power-Up Punch on Celosia's Aegislash. Since Aegislash was a ghost-type Pokémon, the attack had no effect. Still, Mega Lucario's presence emitted the aura to protect the group from being mind-controlled by Aegiaslash. After retrieving the Key Stone, X Mega Evolved his Kangaskhan, who charged in with Mega Lucario to defeat Celosia, who retreated. After Korrina explained she did not feel X was a successor to Mega Evolution, she left off with Lucario. After the group came close to Lumiose City, Trevor had thought of Korrina and realized in order to trigger Mega Evolution, the trainer needs to activate the Key Stone, while the Pokémon has to wear a corresponding Mega Stone, just like Korrina Mega Evolved Lucario.
Once Korrina arrived to the Tower of Mastery, she started attacking Gurkinn for revealing the secrets of Mega Evolution to outsiders and even prepared to Mega Evolve Lucario to teach the old man a lesson. Gurkinn stopped her and explained his reasons for giving the Key Stone without a succession ceremony. After Gurkinn explained his story, Korrina saw an intruder and went after them with Lucario, who Mega Evolved. They faced a Trevenant, so Mega Lucario started battling it while Korrina searched for Gurkinn, who was in trouble. Mega Lucario was knocked down from Trevenant's Bulldoze. In order to counter the attack, Mega Lucario grabbed Trevenant's roots, only to get burned by its Will-O-Wisp attack. Per Gurkinn's request, Mega Lucario released the roots and returned to Korrina's side. Along with Gurkinn's Mega Heracross, Mega Lucario started attacking the roots Trevenant was releasing throughout the tower. In a desperate move, Korrina and Gurkinn had Mega Lucario use Aura Sphere and Mega Heracross to attack the Mega Lucario statue with Pin Missile. The statue crumbled, causing the tower to be demolished.
Once Korrina encountered Chalmers attacking Gurkinn, Korrina Mega Evolved Lucario. Mega Lucario launched Aura Sphere to defeat the Skrelp, who simply regrouped and continued to drown Gurkinn, until Diantha arrived. Facing a thief, Korrina sent Lucario to battle the thief's Binacle, along with Diantha's Gardevoir and Gurkinn's Heracross. Since they were facing Binacle, who used two of their heads at once, Korrina Mega Evolved her Lucario. Later on, Malva met up with Celosia on Route 15 and had thought of Korrina and Mega Lucario, who defeated Celosia and wielded the Key Stone, an item which is a critical part for their plan. Malva also remembered Gurkinn was the one handing out the Key Stones to notable people, like his granddaughter or even the Champion, Diantha.
Korrina, along with Diantha and Gurkinn, came to stop the moving of Xerneas tree. Korrina charged in with Mega Lucario to attack. Korrina chose Celosia to battle. Seeing X Mega Evolved Gengar, Korrina did the same to her Lucario, determined to defeat Celosia. Mega Lucario used Bullet Punch, hitting Aegislash, even pleasing Celosia she was fighting a worthy opponent. Korrina felt angry, as Celosia claimed they were not worthy for Kalos; Korrina had Mega Lucario exchange blows with Aegislash, resulting in a double-knockout.
Celosia had her Aegislash attempt to create an illusion to fool Shauna and take control of her. However, Shauna pretended to be upset, as Korrina's Lucario came and defended her with the aura. After Celosia's Doublade was defeated by Shauna's Shauna's Skitty, Lucario used Foresight and Aura Sphere, which defeated Celosia and Aegislash. Lucario also intimidated Aliana and her Pumpkaboo to let go of Trevor, whom she threatened to hurt.
|Power-Up Punch||Lucky Lucario Was Here|
|Aura Sphere +||X&Y015|
|Bullet Punch||Surrounding Braixen|
|Foresight +||Xerneas Gives|
|+ indicates this Pokémon used this move recently.*|
- indicates this Pokémon normally can't use this move.
- ^ a b c X&Y016
- ^ X&Y006: The Aegislash Agenda
- ^ X&Y007: Lucky Lucario Was Here
- ^ X&Y010: What Does Charmander Do When It Dozes?
- ^ X&Y014
- ^ X&Y015
- ^ X&Y022
- ^ X&Y024: Shooting Frogadier
- ^ X&Y025: Gathering Klefki
- ^ X&Y026: Tying Trevenant
- ^ X&Y027: Changing Gengar
- ^ X&Y028: Surrounding Braixen
- ^ X&Y045: Xerneas Gives