From Bulbapedia, the community-driven Pokémon encyclopedia.
The Sacred Swordsmen are three legendary Pokemon that appear in Kyurem VS. The Sword of Justice. They train Keldeo on how to use Sacred Sword so it can become a Sacred Swordsman.
For more information on these Pokémon’s species, see Cobalion, Virizion, Terrakion, and Keldeo.