A Lucario dies thinking it failed to protect the one trainer it ever loved, and the movie spends its entire runtime proving it wrong. The emotional machinery here is ruthless: Ash has to understand what Lucario couldn't, and you watch a dead Pokémon get saved by the person it spent centuries guarding. The ending doesn't explain itself away with plot logic. It just breaks you with the simple fact that loyalty survives death.

In the town of Lohta, an annual festival honors Aaron, the legendary Wave Leader hero said to have ended a war centuries ago by drawing on the power of the Tree of Beginning. Satoshi and Pikachu win the tournament that picks this year's hero, earning the title and a place at a lavish dance held in the castle. During the celebration, the mythical Pokémon Mew appears and carries Pikachu off. Soon after, Lucario, the Aura Pokémon who once served Aaron, is released from a seal that has held him for centuries. Troubled by the memory of being abandoned by his master, Lucario distrusts humans, yet he alone knows the route to the Tree of Beginning. Satoshi must win his help to rescue Pikachu, and along the way the pair uncover what Mew is after and the long-buried truth behind the legend.