Virizion, Takako Honda, Terrakion, Hiroki Yasumoto, and Cobalion, Koichi Yamadera, belong to a group of Pokémon called the Swords of Justice—a trio who roam the world to help people and Pokémon in need. Their hopeful protégé, Keldeo, Shoko Nakagawa, trains to join them, dreaming of proving himself worthy to wear the mantle of a Sword of Justice. His final challenge before joining is a duel with Kyurem, a formidable Dragon-type whose power can channel the energies of both Reshiram and Zekrom, hidden away in an abandoned mine known as the Full Court. Yet the Swords are wary, doubting whether Keldeo is truly ready for such a trial.
Keldeo, eager but unsteady, sneaks out to the Full Court to confront Kyurem, falsely claiming that he already belongs to the legendary band. Kyurem harshly tests him, breaking Keldeo’s horn and leaving the young Pokémon trembling with fear. The Swords of Justice rush to intervene, but Kyurem’s fury is such that he freezes them all solid in ice. Panicked, Keldeo flees as Kyurem gives chase, vowing that their battle is far from over.
Meanwhile, Ash Ketchum, Iris, and Cilan discover an injured Keldeo on top of their train headed for Roshan City. Kyurem arrives with his minions, several Cryogonal, still determined to settle the score. The confrontation breaks off when the train enters a tunnel, and the trio helps get Keldeo to the Pokémon Center for healing. Outside, they commit to helping Keldeo and freeing the Swords of Justice together.
To pull Kyurem away, Iris seizes a museum zeppelin while Cilan pilots an abandoned mine cart powered by his Stunfisk, drawing Kyurem and the Cryogonal after them. Ash and Keldeo slip away on foot to reach the Full Court and free the Swords of Justice, while the others lead the pursuers on a strategic chase.
Kyurem returns to the mine to resume the fight. Ash heads back toward the Full Court with his Pikachu, Ikue Otani, Pignite, and Boldore to aid in the rescue and liberation of the Swords. The battle intensifies as Kyurem blasts toward Ash and friends, but Keldeo steps in to block and protect them. Though Kyurem already knew that Keldeo had lied about being a Sword of Justice, he still presses the clash, determined to finish the challenge.
In a decisive moment, Keldeo transforms into his Resolute Form and fires a powerful attack. The two dragon and sword clashes shake the Full Court, and the ice imprisoning the Swords begins to crack. Keldeo uses the glowing move, Secret Sword, to strike, managing to slice the opposing blast and save his friends, though the effort leaves him wounded. After the fierce exchange, Keldeo yields, and the duel ends.
The Swords of Justice praise Keldeo for finally embracing the true power of the sword, officially welcoming him as the fourth member of their team. The group retreats from the crumbling Full Court as Kyurem freezes the falling ruins to shield everyone from further harm.
