Keldeo is very reckless, often not listening to his mentors and rushing into battle, like when it attacked Kyurem.
While still in training with the Musketeers, Keldeo was convinced that it was ready to face Kyurem in order to become a Musketeer, but Cobalion refused. Disobeying its mentors, Keldeo walks off to the mines where Kyurem resides and calls it out for a battle, claiming to be a Sacred Swordsman. When it attacked the dragon, it was completely outmatched and had its horn sliced off by Shadow Claw. The battle also resulted in the freezing of the Musketeers, causing Keldeo to flee and Kyurem to pursue him.
Keldeo, weakened from the one-sided battle with Kyurem, fell down a cliff onto a train, which happened to have Ash, Iris and Cilan riding in it. Although it did not trust them at first, it eventually became friends when Ash and co. saved him from Kyurem and its Cryogonal posse. Keldeo then healed up and regained his strength. He told the gang about who he was, and how he aspires to be a Musketeer, like his masters.
Kyurem attacked Keldeo several times, the latter narrowly escaping each time. Ultimately, the battle led back to where the two battled originally, and where Keldeo entered its Resolute Forme, also learning Secret Sword in the process. Keldeo quickly gained the upper hand with improved agility and a combo of Double Team and Focus Blast, but ultimately lost when trying to protect his thawed out masters and friends from a Freeze Shock, with the electrical element causing even more damage. Despite its loss, Keldeo's valor earned it Kyurem's respect, who said it was better to lose a battle than to lose one's friends.
|Focus Blast||Kyurem VS The Sacred Swordsman - Keldeo|
|Double Team||Kyurem VS The Sacred Swordsman - Keldeo|
|Hydro Pump||Kyurem VS The Sacred Swordsman - Keldeo|
|Secret Sword||Kyurem VS The Sacred Swordsman - Keldeo|
|+ indicates this Pokémon used this move recently.*|
- indicates this Pokémon normally can't use this move.