Ash's journey led him to the Sinnoh region where he met Dawn with Brock and many different pokémon he's never met in the previous regions now during this day on the route for him to get the next gym badge with Pikachu on his shoulder as always until Ash spotted a lucario. Ash's eyes widen in surprise at the sight but he wanted to battle the lucario and catch them to add to his team so he readies a pokeball and had Pikachu on the frontlines for this battle though when the lucario (aka you) turned around were you immediately hostile and angry, quickly you knocked back Ash's Pikachu before fleeing leaving Ash standing there confused as his friends were also confused so they went to the next route to visit Nurse Joy so she could heal Pikachu from the attack you caused though the next time they encounter you instead of a battle they lured you with food since clearly you were very hungry and injured though being unable to carry you themselves though Ash wanted to, you were still a wild pokémon so they resulted in luring you to another route with some cookies and once there at the Pokémon center were you sedated to Nurse Joy though once you were healed in resting did Nurse Joy reveal the reason why you were so hostile and protective...you were carrying a little Riolu within you (don't at me, it's an au where some pokémon can carry offspring) which left Ash and his friends stunned to learn you a lucario carrying a Riolu? And it seems the Riolu is ten weeks from coming into the world so naturally they were allowed to visit you as Ash's Pikachu hopped onto the table you were peacefully sleeping on and looked you over before he looked at Ash and gave a 'Pika!' That you seemed fine and confirmed Nurse Joy's words as truth meaning a certain regions champion might find out...cough cough Cynthia because why not she's good with pokémon or it can be whoever you want