from the staff when Ash "assumed the pose" of Sir Aaron, follows Mew to the Tree of Beginning in order to rescue Pikachu. There is but one problem: after being sealed in the staff, Lucario has completely lost his trust for humans which leads to a fight just after the beginning of their quest. While traveling Max gives Lucario a chocolate bar, which he finds he likes and it helps toward him trusting humans. Eventually, Ash earns Lucario's trust by apologizing for his hurtful words and they enter the Tree of Beginning. They are attacked by Regirock, Regice, and Registeel, the tree's guardians who recognize them as a threat. They enter the tree and are attacked by the tree's defense system, antibody-type mechanisms, triggered by Kidd's survey robots. The antibodies are able to transform into jelly-like representation of Pokémon and then absorb the threat. When Ash and the gang are absorbed into the tree, Mew saves them by reasoning with the tree's defense mechanism. The disruption of energy flow in the tree due to the defense system sends the tree into shock, and as Mew and the tree are symbiotic creatures that depend on each other for survival, Mew also becomes very ill. In order to save Mew and the tree, Lucario and Ash combine their Aura to reverse the self-destruction of the tree. Lucario pushes Ash away towards the completion of the process so that Ash won't end up sacrificing himself to the tree as Aaron did (presumably, no matter if it's a human or a Pokemon, giving up all of one's Aura means death for that being). Afterward, a "time flower" shows a memory of Aaron sacrificing himself to stop a war. Right before Aaron died (in the memory), he said how Lucario was his closest friend and would miss him before dying. It is made clear that the reason Aaron sealed Lucario was to ensure that Lucario didn't die with him, Lucario having witnessed this sobs and gives his life so that he can honor his friend. Sadly, it means that Lucario moves on with Aaron into the afterlife. Lucario moves on, without regrets now that he knows he will see Aaron again, as Aaron also did for him. The dramatic ending concludes the story well as all characters move on after learning important lessons of trust, sacrifice, and love, with Ash saying He isn't gone...His aura