The Relentless was an Imperial Star Destroyer that served in the Galactic Empire, under the command of Admiral Kassius Konstantine. It was used by The Grand Inquisitor to hunt down the rebels, Kanan Jarrus and Ezra Bridger. Later, it was used by Darth Vader, Agent Kallus and the Fifth Brother.
Pursuit of the Ghost
On the day of the Galactic Empire's fifteenth anniversary, it was requisitioned by The Grand Inquisitor, the Emperor's Jedi hunter, to give chase to a group of rebellious individuals who tried to smuggle Tseebo off of Lothal. The Inquisitor had placed a XX-23 S-Thread Tracer on rebels' ship Ghost and started pursuing them in hyperspace. When the targets found the tracker, they released the Phantom, because the device had been put on it, and landed on Fort Anaxes. The Relentless followed the signal, and in this way the Ghost managed to escape, while The Grand Inquisitor and his troops faced the rebels on the asteroid, being defeated.
Deceit of Lando Calrissian
Time after, the rebels, together with the smuggler Lando Calrissian, tried to reach Lothal from the space, after acquiring a Puffer pig from the crime lord Azmorigan. Lando had inserted a signature modulator to keep the Ghost safe while meeting Imperial patrols. But because of some problems with the pig, Garazeb Orrelios accidentally disabled it, and so the Relentless was able to identify the ship. Konstantine deployed TIE Fighters and tried to take down the Ghost, but enemy pilot reached Lothal's clouds, leaving TIEs behind and preventing the Relentless to continue the chase.
Siege of Lothal
The Relentless was one of the Star Destroyers chosen by the Empire to siege Lothal. The rebels, after leaving Capital City, asked Lando to help them; he planned a way to reach space without being pursued by Imperial forces. They launched some modified masking trasponders in Lothal's sky, which replicated the signal of their stolen Sentinel-class Shuttle. Konstantine deployed TIE Fighters squadrons to follow the signals, but when he understood his error the Ghost had already left the atmosphere. However, Konstantine and his crew were mollified when Darth Vader revealed that he had already placed a tracker on the shuttle.
The Sith Lord reached the rebels, that had gathered with their allies of Phoenix Squadron, and attacked their ships with his TIE Advanced x1. The Relentless and other Star Destroyers joined Vader when the battle was already lost for the rebels in an attempt to prevent their enemies from escaping. While Vader had succeeded in destroying the rebel command ship Phoenix Home, most of the Rebel Fleet with the exception of the Ghost had already managed to flee into hyperspace. The Relentless and another Star Destroyer attempted to trap the Ghost. However, the freighter's captain Hera Syndulla managed to jump into hyperspace before the Relentless and the other Star Destroyer could activate their tractor beams. Instead of the Ghost, the Imperial captured Vader's TIE Advanced.
Hunting the Rebellion
Following the attack on the Rebel Fleet, the Relentless took part in a hunt for the fleeing rebels throughout the Outer Rim Territories. At a later point, Konstantine and Agent Kallus received a transmission from the former Clone Commander Wolffe that the Ghost Crew were on Seelos. While the Relentless stayed in space to provide back-up, Kallus led a ground assault force of three All Terrain Armored Transports against the Ghost crew and the Clone Troopers Captain Rex, Captain Gregor, and Commander Wolffe. The Relentless was unable to provide support to Kallus' forces during the battle because the ship had received orders to pick up an Inquisitor known as the Fifth Brother in deep space.
Later, the Relentless detected a power surge from an abandoned Republic Medical Station in deep space. The surge had been caused by several crew members of the Ghost who were salvaging medical supplies from the abandoned station. When Konstatine offered to provide reinforcements, the Fifth Brother insisted on going alone. During the ensuing skirmish, he another Inquisitor known as the Seventh Sister nearly succeeded in capturing several rebels including C1-10P, Ezra Bridger and Sabine Wren. However, the rebels were able to escape due to the quick thinking of Garazeb Orrelios.
After the Seventh Sister and the Fifth Brother discovered that the Phoenix Squadron were hiding on Garel, the Relentless was part of the Imperial fleet that attacked Garel. During the battle, the Relentless and its fellow Star Destroyers bombarded the escaping rebel ships and unleashed several TIE Fighters. Under the command of Konstantine, the Relentless also managed to trap the rebel command ship Liberator with its tractor beam projector. However, Hera managed to use the Ghost to knock out the Relentless's projector; allowing the Liberator to flee into space.
The Relentless later led an attack on the Rebel Fleet, which was low on fuel. Konstantine led the attack from the helm of the Relentless. When the ship's scanners picked up the Ghost, Konstantine recognized it as the vessel that had raided the Imperial fuel depot at Horizon Base. Realizing that the rebels were low on fuel, he ordered the Relentless and its TIEs escorts to prevent the Ghost from landing. Despite their best efforts, the Ghost managed to land due to the timely intervention of Ketsu Onyo's starship Shadow Caster. After receiving intelligence from Chopper and the inventory droid AP-5, the Rebel Fleet fled to Atollon, a safe system with no Imperial presence.