The Swords of Justice (Japanese: 聖剣士Sacred Swordsmen) is a collective term to refer to the quartet of Cobalion, Terrakion, Virizion, and Keldeo. They are also commonly referred to by fans as the Legendary musketeers.
The group is based on the French novel The Three Musketeers by Alexandre Dumas, père. Cobalion represents Athos, the oldest and de facto leader of the group. Terrakion represents Porthos, the strongest, heaviest, and largest member of the group. Virizion represents Aramis, the most feminine, vain, and romantic member of the group. Keldeo represents d'Artagnan, the youngest by far and the latest addition to the group.
The Swords of Justice have challenged humans according the legend in order to protect other Pokémon from losing their homes to human expansion. According to Legend, three Swords of Justice distrust humans because of the war that endangered the Pokémon living in Unova.
The reason is because of war between two human factions, which resulted in a forest fire in the Moor of Icirrus. The lives of many wild Pokémon that lived there were endangered because of it. Ensnared by the smoke, they could not escape and their demise seemed certain, until three figures appeared.
Terrakion shaped the earth and created passage by which to escape, Virizion used its speed to shield the Pokémon from sparks and embers, while their leader, Cobalion, ushered Pokémon to safety. Despite their efforts, the forest eventually burned to the ground. However, amongst the ashes, the three came across a lone Pokémon known as Keldeo who was separated from its parents. The trio adopted Keldeo into their group and taught it the knowledge and moves necessary in order to survive. Over time, Keldeo began to surpass its teachers before leaving the forest, though it is unknown why it left.
The trio proceeded to fight back the armies, overwhelming them with their combined might. Legends of them continue to be told today, and it has been said that if human conflict ever again threatened to safety of Pokémon, that they would return to quell the fighting and preserve a climate of peace.
The player can encounter Cobalion, Terrakion, and Virizion at the Pathless Plain while soaring in the sky as long as there are three Pokémon with 510 EVs in the player's party. Cobalion appears on Wednesday, Friday, and Sunday; Terrakion appears on Tuesday and Saturday; and Virizion appears on Monday and Thursday.
Pokémon Ultra Sun and Ultra Moon
The player can encounter Cobalion, Terrakion, and Virizion in the Ultra Space Wilds' Rocky World dimension by traveling through green warp holes in Ultra Warp Ride.
The Swords of Justice all made their anime debuts in Kyurem VS. The Sword of Justice. Cobalion, Terrakion, and Virizion train their youngest member, Keldeo, but before the Colt Pokémon finishes its training, it decides to test its strength against Kyurem. The Boundary Pokémon proves to be too much for Keldeo, who flees from the battle, but is actively pursued by Kyurem, who wants to finish their match. Keldeo is then found by Ash and his friends, who help it to end the battle with Kyurem.
In the manga
Cobalion, Terrakion, and Virizion in Pokémon Adventures
Virizion debuted in A Direct Attack and a Daunting Defense, where it attacks Black and White as they cross the Skyarrow Bridge, cutting up their clothing. After learning about the date of the Pokémon League's date being pushed up, Black decides to capture the Swords of Justice in a desperate attempt to convince Drayden to give him entry into the League without an eighth Gym Badge. His travels take him to Mistralton Cave, where he meets Shoko, a young girl who's friend, Trish, had gone into the cave to capture the Swords of Justice herself.
When they hear a cry of pain, Black and Shoko enter the cave to find that Trish had been defeated and captured by Terrakion and Virizion. Black manages to get Trish out of Terrakion and Virizion's grasp with the help of Bo. When Trish wakes up, she decides to battle and capture the two Pokémon again, but is interrupted by the third Pokémon, Cobalion. Cobalion's appearance startles Trish into dropping her torches, causing a fire to start inside of the cave. Using teamwork, Cobalion, Virizion, and Terrakion put out the flames as well as capture Shoko and Trish's Pokémon so that they can be freed from their Trainers. Black tracks them using Musha's dream eating abilities, and he manages to free the girls' Pokémon after telling the three legends that Trish and Shoko truly love their Pokémon. Cobalion, Virizion, and Terrakion then disappear into the distance, much to Black's disappointment since he never captured them.
Later, the Swords of Justice are seen communicating with each other through telepathy as they travel towards Pledge Grove to meet their apprentice, Keldeo. During their journey, the Shadow Triad catch sight of them and recognize them before planning to catch them, but Cobalion uses Metal Burst on the Shadow Triad before leading Terrakion and Virizion to safety. They meet Keldeo as promised, and teach it the move Sacred Sword, allowing it to leave a cut on the stone and complete its training. After Keldeo accomplishes this, Cobalion decides that all four of them would apprehend the Shadow Triad, as it knew that the Shadow Triad are up to no good and cannot be ignored.
They travel to the P2 Laboratory, where the Shadow Triad and the Striaton Gym Leaders, Cilan, Cress, and Chili, are locked in combat. From the expressions on each sides' Pokémon, Keldeo determines the Striaton Gym Leaders to be the good side. Keldeo rushes in to defeat the Shadow Triad's Pokémon, but gets captured in the process. Fortunately, Cobalion, Terrakion and Virizion come to the rescue by swinging their swords at both trios, defeating both sides before deciding to leave. Although defeated, the Shadow Triad refuse to back down and activate the P2 Lab's doors and have their secret weapon fire a laser at Keldeo. Keldeo is protected by its three mentors, who are frozen by the laser and proceed to sink into the waters below.
Two years later, Keldeo was encountered by Blake and Whitley during a run to fill the Pokédex with data. After having been lured out by Whitley's Foongy's Sweet Scent, Keldeo lashed out at the two and attacked them with its sword. Blake managed to dodge, but accidentally stepped too far and fell down a cliff. A while later, Keldeo agreed to join Blake's team, and is nicknamed Kelden.
The Swords of Justice, excluding Keldeo, are captured by the organization Great Gavel and turned into Burst Hearts. Their Burst Hearts are then given to the three generals: Amu, Ganku, and Rovy.
In Generation V, the Swords of Justice have their own battle transition, like the Tao trio and the Forces of Nature. The screen will pause, fade to black, and then a sword will slash through the screen as the glass breaks into pieces and the battle begins.