Form: Jar'Kai

"Perhaps you would like to learn something before you die. The use of two blades, one to support the other, can be traced back thousands of years and was common to both of our species. The invention of lightsabers has done nothing to lessen the effectiveness of this strategy—as you are about to learn."
-Boc Aseca to Kyle Katarn

Jar'Kai is a subform of Niman and is one of the oldest forms of lightsaber combat, a dual blade wielding technique

With the two single blades, a wielder who could maintain a strong offense, as two blades could keep an opponent wondering which one to shift towards to defend against. One of the blades in the wielder's hands was used for attacking while the other one was used for defending, such as parrying, or for more offensive purposes. It is also useful against more then one user as one blade can only be in one place at one time. However, it is not without its weaknesses.

A user of Jar'Kai who lost the offensive was at a disadvantage to a single hilt user, especially a powerful one. The use of two blades prevents the user from putting all his weight behind a defensive block, thus weakening one's defense considerably. A physically stronger opponent could simply batter a Jar'Kai user until their guard finally gave way and when using dual sabers, a practitioner would have a limited range of motion; for example, a forward overhead chop would bring their second blade back up at the user and potentially split them from groin to head. It is also harder to control and less precise, thus not ideal for delicate situations as collateral damage is likely to happen.

History
Jar'Kai was originally the name of a city on Atrisia. Here were crafted the original Jar'Kai dueling sabers, which were wielded by the Yovshin Swordsmen. The Swordsmen, wielding one saber in each hand, invented the Jar'Kai style.
Similar was the style developed by the Royale Macheteros of the Kashi Mer monarchy. The latter technique was used by the Legions of Lettow, during the First Great Schism, who called it Niman after a dual triumvirate of the Kashi deities.

Ancient Niman relied on steel blades, as lightsabers had not yet been invented, but the style could be used with a great variety of weapons.
The application of Jar'Kai also exists as a tactic instead of a completely independent style, one example includes Sora Bulq, who utilized Jar'Kai in conjunction with Vaapad. Also, Anakin Skywalker's Jar'Kai application against Count Dooku on Geonosis was actually based on Ataru swordplay. Unfortunately, as Skywalker had not received advanced training in either the Jar'Kai or Form IV, Dooku was easily able to break through Anakin's array of weapons.