ES-04, whose alias was Firebrand, was a human female Elite Squad Trooper serving within the Galactic Empire during the early period of the Imperial Era. She was brought into service via Project War-Mantle alongside her fellow soldiers, and Vice Admiral Edmon Rampart considered her to be among the most skilled fighters in the galaxy. As a member of Clone Commander CT-9904's Elite Squad, ES-04 took part in the massacre of civilians following the demise of ES-01, who was killed for disobeying the commander's directives.
Following the end of the Galactic Republic and the establishment of the Galactic Empire in 19 BBY, the newly formed Imperial Military aimed to reorganize its forces. Through an initiative called Project War-Mantle, Vice Admiral Edmon Rampart began recruiting human conscripts as potential replacements for clone troopers, who had been the standard infantry of the Grand Army of the Republic. The individual who would become known as ES-04, also going by the name Firebrand, was one of these recruits, becoming one of the first Elite Squad Troopers in the Empire. The Vice Admiral considered her to be one of the best soldiers in the galaxy, taking pride in his troops.
Along with her comrades ES-01, ES-02, and ES-03, ES-04 was brought by Rampart to the Tipoca City Military Complex located on Kamino, where the squad was placed under the command of clone commando CT-9904 "Crosshair," a modified clone known for his abilities as a sharpshooter. After a medical evaluation performed by Kaminoan droids, the group was assigned by Governor Wilhuff Tarkin to eliminate Saw Gerrera, a rebel leader situated on the planet Onderon. Tarkin, wanting to assess the squad's effectiveness, ordered them to destroy Gerrera's camp and eradicate any resistance.
Upon arriving at Onderon aboard a Nu-class attack/transport shuttle, ES-04 and her squadmates made their way into the planet's jungles and located the rebel camp, although Gerrera was not present. As Crosshair led the main assault on the insurgents, ES-04 used a BT X-42 heavy flame projector to flank the enemy, eliminating several fighters as they retreated towards an LAAT/le patrol gunship. Her subsequent target, the occupants of the gunship's cabin, were saved from her stream of fire when the ship's pilot sealed the vessel's hatch doors. However, a precise shot from one of the Elites eliminated the pilot, leaving the ship vulnerable.
With only refugees remaining, ES-01 suggested taking them as prisoners, but Crosshair refused, shooting the trooper for refusing to eliminate all members of the camp. Following the orders of their clone commander, ES-04 and the rest of the squad turned their weapons on the huddled refugees, killing them all. Upon returning to Kamino, Tarkin and Rampart praised ES-04 and the rest of the squad for their dedication, anticipating their future victories in the name of the Empire. Afterwards, the squad went to their barracks, which had previously been occupied by Crosshair's former team, Clone Force 99.
After being informed by scavengers on Bracca that Clone Force 99 had been sighted on the planet, they were brought to search for them along with the rest of their squad and three Empire ships worth of stormtroopers.
ES-04 and her squad were assigned the task of capturing Clone Force 99 on Kamino. Crosshair engaged in a discussion with Hunter before trying to negotiate a truce with them by instructing the Elite Squad to stand down. When they refused and attacked Crosshair, he fired a shot that bounced around the room, resulting in their deaths.
ES-04 was a human female with dark skin, brown eyes, and auburn hair. She expressed disappointment that the end of the Clone Wars meant fewer enemies to fight in the galaxy, and therefore willingly joined the Imperial Military. She demonstrated a level of loyalty to the Empire that Vice Admiral Rampart greatly valued, and she was willing to follow orders regardless of any moral concerns.
Vice Admiral Rampart regarded ES-04 and her squad as some of the best soldiers in the galaxy and spoke highly of their abilities to others within the Empire. Despite the belief of Kaminoan Prime Minister Lama Su, who oversaw the creation of clone troopers for the Republic, that conscripted soldiers could never achieve the same level of skill as fighters bred for war, Rampart disagreed, believing that troops like ES-04 would acquire the necessary skills over time.
Like the other Elites, ES-04 wore modified Phase II clone trooper armor, tailored to fit her specific body type. The black armor featured a helmet with green lenses. ES-04 carried a BT X-42 heavy flame projector into battle, a unique weapon within her Elite Squad.
ES-04 debuted in "Replacements," the third episode of the first season of the animated series Star Wars: The Bad Batch, which was released on May 14, 2021. Her designation is provided in the episode's end credits, which also note that the character's voice is provided by actress Dahéli Hall. The descriptive audio for the episode on Disney+ incorrectly labels the trooper with the flamethrower on Onderon as Crosshair, when it is actually ES-04.