Clarissa encountered Riolu on Kanto Route One and saved him with the help of Charmander. After chasing after Team Rocket, Clarissa decided to capture the Baby-Pokemon.
Riolu later evolved into Lucario during Clarissa's gym battle against her grandfather.
Lucario made a surprise return to Clarissa's team and saved her from getting hurt. He was used in the battle against Anabel and Mega Evolved for the first time without losing control.
After his trainer's petrification, Lucario is under the command of Jax Darksoul. After this he does not return to Korrina for training and instead is sent to Benji's.
Lucario is calm and powerful Pokemon who holds a lot of pride. He has a strong affection for his trainer, retaining the bond throughout the journey. Although they have a strong bond, Lucario is very jealous of how close Charizard is to his trainer. This resulted in Mega Evolution not being stable enough and let to him lashing out at Clarissa. Although he was defeated by Charizard, Clarissa was traumatized and decided to send him back to Benji's. Their bond became stronger over time and was able to Mega Evolve with Clarissa. When he was sent to control his Mega Form, Lucario trained under the guidance of Korrina. Eventually he came to understand that no matter what, Charizard will always be Clarissa's closest Pokémon but it doesn't mean he isn't valued.
