As Ash arrives at Shalour City, eager to battle Gym Leader Korrina and her Lucario, he stopped at the Pokemon center to come up with a strategy to defeat Korrina. Previously, Lucario had defeated Pikachu in a Pokemon battle using Aura Sphere. Ash plans to use Pikachu again when the time comes to battle Lucario.
Clemont, Bonnie and Serena saw the serious and focused look on his face, Serena said, "Ash, it will be all right. Pikachu's gotten a lot stronger since the battle with Lucario." Clemont agreed, saying, "I agree with Serena." Ash then thought to himself, "Yeah, I just have to believe in my Pokemon." He thanked Clemont and Serena for their encouragement and proceeded to prepare for the gym battle, which is scheduled to take place in few moments.
As Ash wraps up his special training, he says to his Pokemon, "You're all gonna do great later!" His Pokemon smiled in glee. Before he left the Pokemon center, Ash has Nurse Joy rest his Pokemon for a while. In a few moments, Ash and friends have arrived at the Shalour City Gym. Korrina and Lucario had been waiting in the gym for Ash. Korrina then said, "We've been waiting for you, Ash. Are you ready for a very intense battle?" Ash replied, "Sure I am!" In a few minutes, Ash and Korrina had taken up their respective battle positions.
The referee declared the three-on-three battle started. Korrina calls out Mienfoo and Ash sends out Fletchinder. The battle began with Fletchinder using Flame Charge, increasing its speed in the process. Mienfoo dodges Flame Charge and tries to use Jump Kick which missed its target and injured itself brutally. Fletchinder comes back with another Flame Charge and knocks out Mienfoo while increasing its speed again.
The referee declares Mienfoo unable to battle and the winner being Fletchinder. Korrina calls back Mienfoo, complimenting it for a job well done. She claims that Ash is still no match for her even though he got stronger and she immediately calls out Machoke. Ash calls back Fletchinder and replaced it with Hawlucha. The battle continues. The battle started off with Machoke's Karate Chop, but the Karate Chop was blocked by Hawlucha's wings. Machoke was then hit hard with Hawlucha's Karate Chop. The two Pokemon exchanged Karate Chops with each other for the next half an hour. After what seemed like a see saw match, Hawlucha came from behind with a Flying Press and subsequently knocked Machoke out. The referee declared Machoke unable to battle. Korrina called Machoke back with a smile. Ash then said, "Good job Hawlucha! You were so awesome!"
Korrina then called out Lucario and subsequently had it Mega Evolve. Ash decided to continue the battle with Hawlucha. As the third round begins, Lucario started off with Aura Sphere, overpowering Hawlucha's Flying Press and hitting it hard. Hawlucha tried to knock it out with High Jump Kick but it missed its target and caused a heavy recoil damage to Hawlucha. Lucario then knocked Hawlucha out with a powerful Force Palm. Ash calls back Hawlucha and sends out Fletchinder. The battle may seem like Ash is winning, but before Fletchinder could land a hit on Lucario, it got knocked out by Aura Sphere. Ash calls back Fletchinder, complimenting it for a job well done.
Ash then sends out Pikachu, saying, "This is it, Korrina." Korrina replied, "Yeah, the rematch between Pikachu and Lucario." Lucario used Aura Sphere and landed a hard blow on Pikachu. Pikachu stood right back up and used Thunderbolt. Although it caused some damage to Lucario, it just wasn't enough. Lucario then used Bone Rush and landed a devastating blow on Pikachu. Pikachu laid on the battlefield, it looked like it wasn't able to battle, but then Ash shouted, "Pikachu! You can do it! Stand up and defeat Lucario!" Because of Ash's words, Pikachu mustered enough strength to stand up, Korrina said, "It's over, Lucario use Aura Sphere!" Lucario went ahead and used Aura Sphere. Ash then called a Thunderbolt as a counter attack. A miracle indeed, Thunderbolt managed to overpowered Aura Sphere and it hit Lucario hard. Lucario has been defeated.
The referee declared Ash the victor of the gym battle. Ash proudly complimented Pikachu on how awesome it was, his friends congratulated him on an awesomely intense battle of wills and another badge earned. As Korrina walked up to Ash, she proudly presented the Knuckle Badge to Ash, congratulating him on his victory.
Korrina also suggested that Ash head down to Coumarine City for his next gym battle and Ash made a decision to there thereafter. As Ash leaves the gym to go to Coumarine City, Korrina wished Ash good luck and bid him farewell. Ash replied, "Thanks Korrina! The same to you and Lucario!" He then left wtih his friends for Coumarine City as the journey continues.