Sword

A Sword was a long, sharpened piece of metal with a handle and/or hilt, that was used as a close-quarters weapon and appeared in Batman: Arkham City, Batman: Arkham Origins, and Batman: Arkham Knight.

Arkham Origins Incident
Deathstroke attempted to use his pair of specialized swords in order to assassinate Batman on Christmas Eve to gain "Black Mask's" 50 million dollar reward. Both swords were eventually thrown aside by Batman before, during, and after their showdown. Also in Shiva's Most Wanted Side Mission, there were Ninjas that she commanded. In addition, in the boss battle when the Martial Artists appeared, Shiva used her own sword to fight Batman.

Arkham City Incident
Almost every member of the League of Assassins wielded swords. The infantry ninjas used those weapons against Batman and the entrance of their headquarters was accessible by any fitting sword, and was used like a key. Ra's al Ghul used his sword in his fight with Batman and to kill Hugo Strange. Ra's was "killed" after he tried to impale both Batman and himself with it. Talia al Ghul used her sword, hoping to kill "Joker", and Batman used it to defeat Clayface.

Arkham Knight Incident
In the Arkham Knight's Army, there were soldiers that looked like ninjas that held swords. Batman had newer moves to battle against those enemies.

Ra's Swords and Talia's Sword from Arkham City can be found in the GCPD Evidence Room and it is revealed they were recovered from Arkham City following Joker's death.

In the The Season of Infamy DLC mission The Shadow War, Ra's al Ghul wields a sword during his brief fight with Batman, should Batman choose to resurrect him.

Gameplay
Enemies that use swords first appeared in Arkham City as female ninjas of the League of Assassins and sand ninjas in Ra's al Ghul's test, and Ra's al Ghul himself (in combat challenges, however, only female ninjas are present). They only attack using swords. Their attacks are counterable if they swing from above and uncounterable if they swing from below. When they launch an uncounterable attack, you have to evade it, or using the Blade Dodge or the Blade Dodge Takedown against it. Ninjas are the quickest enemies because it's hard for Batman to strike them unharmed when they're performing a counterable attack (it's somewhat easier with other quicker characters, especially Catwoman), and they can dodge most gadget projectiles (except when they can be hit with the REC sometimes) as well as Aerial Attacks and Ground Pounds. Their swords cannot be separated from them. The Special Combo Takedown can be performed on them if you wish to eliminate them quickly.

In Arkham Origins female ninjas are still the only enemies who use swords and they attack the same way as before. Female ninjas also appear as normal armed enemies in predator maps. In the main story, Deathstroke also uses a sword to fight after his staff is destroyed by Batman; his fighting style, however, is completely different from ninjas.

In Arkham Knight, the main type of enemy Batman fights in the main story that use swords are known as Combat Experts. They have more combat maneuver abilities compared to ninjas, such as jumping on each other and striking from above with a counterable attack. They still attack only with their swords. Combat Experts are militiamen employed by Scarecrow and the Arkham Knight, but Penguin also has his own versions that are sword-wielding shirtless henchmen. In the Shadow War story, female ninjas reprise their role, but this time around, they also do hand-to-hand combat with a series of quick counterable strikes, rather than just sword attacks.

Trivia

 * All blades in both games (besides Ra's' and Talia's) looked very much like the real life, Chokuto, which is a straight Japanese sword that was used prior to the 10th Century. Deathstroke's pair looked much like a Chokuto too, but with a special hilt that fitted his armor's appearance.
 * Technically, Batman used Talia's Sword like a gadget in Arkham City in his battle against Clayface at the Monarch Theatre.
 * It was hinted that the Arkham Knight possessed a sword. A close examination of his side revealed something that resembled a handle or a hilt, which improved the chances that he possessed one.