Mythical Pokémon Keldeo wishes to join the Swords of Justice, a group of Pokémon traveling around the world, helping out those in need. To do so he must first harness the power of his horn and learn the move Sacred Sword, and he decides to challenge Kyurem, a Legendary Dragon residing in an abandoned mine located within an icy crater. Confident as he is at first, it soon occurs to Keldeo that he is not yet ready for the fight.

Meanwhile, as Satoshi and his friends travel across the Unova region, they stumble across an injured Keldeo. At the same time, Kyurem goes on a rampage, drawing energy from other Legendary Pokémon and disturbing the balance of power in the entire region.

Now backed by his new friends, Keldeo must overcome his weaknesses and face Kyurem once again, now with the fate of the world at stake.