Having been born at the same time as Reshiram and Zekrom, Kyurem is considered the strongest Dragon-type Pokémon in the world. It can harness the powers of both Reshiram and Zekrom at will, allowing it to transform into White Kyurem and Black Kyurem respectively. According to Keldeo, one cannot become a Sword of Justice until one defeats Kyurem, who the Colt Pokémon is eager to fight against in order to become a member of that position.
As Black Kyurem
Residing in the abandoned mines of a mountain sanctuary named Full Court, Kyurem was challenged to a battle by Keldeo, who claimed to be a Sword of Justice but in truth was training to become one. The Boundary Pokémon engaged Keldeo in battle, and although the Colt Pokémon managed to land a hit on Kyurem, the latter soon proved to be too strong for Keldeo, and the fight escalated with Kyurem breaking off Keldeo's horn with a Shadow Claw attack. Terrakion, who had observed the battle nearby, attempted to stop the fight to help Keldeo, despite Cobalion's warnings. Enraged by the intrusion, Kyurem shifted into White Kyurem and used Ice Burn on Cobalion, Virizion, and Terrakion, locking them in a block of ice to prevent further interference. Keldeo was overcome with fear and fled during the middle of the battle. Furious, Kyurem began pursuing the Colt Pokémon, angrily declaring that their battle was not over.
Determined to finish their battle, Kyurem, aided by its Cryogonal followers, relentlessly hunted down Keldeo, but was stalled by Ash, Iris, and Cilan, who found the Colt Pokémon and befriended it. After being lured away from Keldeo by Iris, and later Cilan, Kyurem returned to the abandoned mines, which Ash would later enter in his attempt to free the trapped Swords of Justice when Keldeo was once again gripped with fear. Kyurem, enraged by the intrusion of a human in its lair, confronted Ash, who was striking at the ice that held the Swords of Justice to free them. When Ash refused to leave, the Boundary Pokémon attacked him with Dragon Pulse, but the strike was blocked by Keldeo, who finally gained the courage to face Kyurem.
Keldeo admitted to Kyurem that it lied about being a Sword of Justice and did so in order to do battle with the Boundary Pokémon, but Kyurem revealed that it already knew that Keldeo was a liar from the start and then demanded that they ended their battle. Through Ash's support, Keldeo transformed into its Resolute Form and proceeded with its battle against Kyurem, with the Boundary Pokémon still proving to be too much for Keldeo. As it seemed that Kyurem won the battle by freezing Keldeo solid using Freeze Shock as Black Kyurem, Keldeo broke free and was able to learn a move called Secret Sword. With it, the Colt Pokémon landed a direct hit on Kyurem.
As regular Kyurem
Pleased by this turn of events, and witnessing Keldeo's true power, Kyurem attacked at full strength by unleashing another Freeze Shock attack, which Keldeo blocked, but caused the attack to threaten Ash, Iris, Cilan, and the now freed Swords of Justice. Keldeo leaped in and split the Freeze Shock in half with Secret Sword, preventing the attack from hitting its friends, but took major damage in the process. This resulted in the Colt Pokémon collapsing, and Kyurem pinned Keldeo down by its horn. The Colt Pokémon admitted defeat, but instead of finishing the battle, Kyurem reverted to its normal form, impressed that Keldeo chose to protect its friends over winning the fight, earning Kyurem's respect. When the mines began to collapse from the damage it sustained from the battle, Kyurem changed into White Kyurem and simply froze the collapsing pieces into place, preventing the destruction of the mines and creating an ice castle to live in, while the Swords of Justice, Keldeo, and the others escaped to safety. Kyurem then shifted back into its normal form and lumbered back into its lair without a word.
Personality and characteristics
Kyurem is considered the strongest Dragon-type Pokémon in the world, as it has the ability to transform into Black Kyurem and White Kyurem at will, utilizing the powers of Zekrom and Reshiram, respectively, while in those forms. Destructive as it can be, however, it chooses to live in seclusion in Full Court, an abandoned mine, with a group of Cryogonal who serve it.
Although it prefers to stay away from others, when challenged to a battle, Kyurem will readily accept the challenge. Kyurem hates for its battles to be interrupted, and will attack anyone that attempts to stop a fight it is engaged in. If an opponent runs away from a fight, Kyurem will chase them down with relentless fury until it defeats the opponent.
It also possesses a dislike for humans who trespass into its lair, as it was hostile towards Ash and was willing to destroy him when the Trainer refused to leave without freeing the Swords of Justice trapped in ice. Kyurem has the ability to tell if an opponent is not using their full strength, and will continuously pressure them into using it. Despite this, it is shown to have a sense of honor, as Kyurem valued Keldeo's courage for saving its friends instead of winning the battle the Colt Pokémon aimed to achieve in order to become a Sword of Justice.