Kyurem is the strongest Dragon type Pokémon in the world. It was born at the same time as Zekrom and Reshiram.
It possesses the strongest genes and its body is constantly emitting a bitter chill. Kyurem lives in an abandoned mine up over the mountains near Roshan. It's said to have never been seen leaving there until it chased after
Keldeo.
Kyurem is able to speak to humans.
Keldeo went to challenge
Kyurem on its own despite not being able to use its sword yet and against the council of the Sacred Swordsman. During the battle against Kyruem,
Keldeo learned that it was still too weak to face
Kyurem and it got its horn broken off and it fled because it was scared.
Virizion,
Terrakion and
Cobalion came to rescue
Keldeo but they were frozen in ice by
Kyurem.
After falling on the train that
Ash Ketchum and his friends were traveling on, it befriended them and with their encouragement,
Keldeo decided to face
Kyurem once more. During that battle,
Keldeo learned to use its sword properly and was able to prove to
Kyurem that it was a strong Pokémon after all.
Kyurem complemented
Keldeo on a nice sword and putting the safety of its friends first before accepting that it won the battle against
Keldeo. After
Keldeo proved to be worthy to become a Sacred Swordsman,
Virizion,
Terrakion and
Cobalion had no objections and agreed that
Keldeo should join them.