The Relentless was a member of the Imperial I-class Star Destroyer family, serving the Imperial Navy throughout the duration of the Galactic Civil War.
Once the Galactic Empire uncovered the coordinates of a makeshift construction zone utilized by the Rebel Alliance for B-wing starfighters, the Relentless was ordered to intervene and prevent the area's evacuation. Shortly after its arrival, the vessel deployed TIE Fighters along with TIE Bombers to engage the escaping Rebel vessels. Nevertheless, the TIE fighter attacks faced fierce resistance from a squadron of Rebel X-wings belonging to Red Squadron, commanded by Commander Keyan Farlander. Ultimately, the B-wing prototypes successfully jumped to hyperspace.
Sometime later, the people of Habassa became allies of the Rebellion. To facilitate the destruction of the Relentless, the Rebels and Habassa conspired to set a trap for the Frigate Mayhem in order to seize it.
Soon after, the Rebels successfully captured some Imperial officers en route to the Mayhem. Through interrogation, they acquired valuable intelligence concerning the Relentless and its associated task force. With this information, they devised a strategy to strike at the Relentless, beginning with the capture of the Mayhem and the annihilation of the Frigate Juvaini. With its support fleet neutralized, the Relentless was rendered susceptible to attack.
Following a series of skirmishes, the Relentless suffered significant losses to its TIE fighter reserves. Rebel forces intercepted and destroyed the BFF-1 bulk freighters named Dotermin and Sornsen, which were attempting to replenish its supplies. A subsequent attempt to deliver replacement TIE Interceptors was thwarted in the skies above Sunaj IV.
Finally, the Rebels launched a direct assault in advance of their exodus to Hoth. B-wings from Red Squadron, once more under the leadership of Keyan Farlander, were tasked with engaging the Relentless, while A-wings from Blue Squadron served as escorts. After employing proton torpedoes to disable its shields, Red Squadron relentlessly bombarded the Relentless with laser cannon fire, ultimately resulting in its destruction.
The Relentless makes its sole appearance in the X-wing game. However, multiple Star Destroyers have shared the name Relentless, with at least one existing during the same period.
Whether the game developers intended the ship's inclusion to be a cameo of that specific vessel remains uncertain, as the narrative structure did not facilitate any explicit connections.