Subject 1138, known as "Starkiller," was a clone derived from Darth Vader's secret apprentice. He wielded two lightsabers that were specifically made to be his armaments. The Dark Lord presented these lightsabers to the clone during his training on the planet of Kamino. Starkiller employed them during his escape attempt, which occurred immediately after Vader dismissed him as yet another failure among many imperfect clones.
The dual weapons of Subject 1138 were designed to facilitate the training of Galen Marek's clone in lightsaber combat. They belonged to the second set of lightsabers that Darth Vader granted to the clones who demonstrated significant progress in their trials. Consequently, each of these lightsabers contained a synthetic crystal, enabling them to generate a red blade. Their design was a modified iteration of the initial set of lightsabers, numerous copies of which were utilized by the clones who were deemed unsuccessful early in their training.
Similar to their counterparts, Starkiller's lightsabers featured a transparent hilt that showcased the fluctuating energy of the blade within. The hilts were equipped with black plates, and the activator was a simple red button positioned on a silver ring around the hilt, roughly halfway down its length. The emitters incorporated a slanted, wrap-around guard, giving them an aesthetic resemblance to emitter shrouds, rather than the standard emitters found on the original stock design.
As with his clone predecessors, Starkiller was imbued with the knowledge and skills of his genetic template through memory flashes. Consequently, he inherited the original Starkiller's inclination for the Form V/Shien-style reverse grip, as well as the Form IV/Ataru and Form VI/Niman fighting styles. These combat forms ultimately allowed the clone to master the Jar'Kai technique, in which Starkiller identified both advantages and disadvantages. He recognized that wielding dual-lightsabers enhanced his overall combat prowess, but also acknowledged that Jar'Kai weakened his attacks by preventing him from gripping a lightsaber with both hands.
Having progressed significantly through a series of trials, Subject 1138, known as "Starkiller," was presented with his lightsabers by his Master and creator, the Sith Lord Darth Vader, in 1 BBY. As one of numerous clones created and tested to replace the Dark Lord's original apprentice, Galen Marek, Starkiller's initial task with his new weapons involved destroying a group of training droids disguised as Rebel troopers. Displaying no sympathy for the Rebel Alliance that Starkiller's progenitor had helped establish, the clone effortlessly destroyed the faux-troopers. However, he found himself unable to bring his lightsabers down on a holodroid that assumed the form of Captain Juno Eclipse. This unsuccessful training session, coupled with the resurfacing memories of the Human woman with whom Marek had fallen in love, prompted Starkiller to rebel against his creator by escaping from Kamino, taking his lightsabers along with him.
While traversing the galaxy in pursuit of Eclipse, Starkiller encountered numerous opportunities to employ his dual-lightsabers in combat. On Cato Neimoidia, the clone eliminated countless stormtroopers and various other Imperial soldiers in Tarko-se, shortly before wielding his lightsabers against Baron Merillion Tarko's Gorog. Subsequently, he altered the color of the blades to blue when the Jedi General Rahm Kota gifted him with two crystals—relics from the Clone Wars—to replace Starkiller's synthetic ones.
Soon after the alteration, Starkiller utilized the lightsabers against a squadron of Terror Troopers and Terror Droids that had infiltrated the Salvation, the Alliance Fleet flagship commanded by Captain Eclipse. Having cleared the starship of the Terror units, the clone employed his lightsabers against various Imperial soldiers, including Saber Guardsmen and Sith Acolytes, during the Assault on Kamino. In Timira City, the cloning facility where Starkiller was created, his lightsabers left a trail of destruction; the clone decimated much of the Imperial garrison as he infiltrated the inner workings of Timira City.
Prior to engaging Darth Vader in a lightsaber duel, Starkiller was compelled to wield his lightsabers against a group of aberrant clones, all of whom originated from Galen Marek's genetic material. When Vader threatened to strangle Juno Eclipse to death using the Force, Starkiller surrendered his weapons as a sign of submission. Eclipse discreetly retrieved one of the lightsabers and attempted to assassinate the Sith Lord, damaging the control panel on Vader's armor in the process. In retaliation, Vader separated the lightsaber from Eclipse with a powerful Force Push. Reclaiming both lightsabers through telekinesis, Starkiller was consumed by rage due to Vader's assault on Eclipse. During the final phase of their duel, Vader employed a Force blast to disarm Starkiller, completely destroying both lightsabers. Despite the loss of his weapons, Starkiller managed to subdue Vader using Force lightning and seize his lightsaber. Vader was subsequently apprehended by Kota's soldiers, while his lightsaber remained in Starkiller's possession.
According to the novelization, which serves as the most canonically relevant source regarding these weapons, both lightsabers are obliterated during the Assault on Kamino when Vader uses the Force to blast them from Starkiller's hands, causing them to shatter. However, in the video game and graphic novelization, Starkiller's lightsabers remain intact at the conclusion of the battle.