Coyerti was a planet located at the edge of the Mid Rim Territories, with one moon in its orbit. Its terrain included hills and valleys, with jungle among them. The planet's atmosphere was humid with a heavy vegetal smell that reacted to blaster bolts, creating a pungent smell. Coyerti was rich in plant and animal life, having thick-leaved trees and red ferns as well as being home to a sentient species of the same name.
Coyerti was the subject of some debate among members of the Galactic Republic's senate during the years prior to the Clone Wars, which begun in 22 BBY. It was argued a shipping lane should be opened between Coyerti and the planet Malastare to transport permacrete.
In 19 BBY, the Republic transitioned into the Galactic Empire. The Empire came to use Coyerti as a research outpost as the planet was rich in plant and animal life, making it a perfect testing and development ground for the Empire's biological weapons. The poisons were manufactured at an Imperial Distillery in Coyerti's hills and deployed on the planet's ecosystem, leaving behind bogs of rotting trees and composting debris. In the meantime, the native Coyerti fought back at the Imperial occupiers, wasting Imperial resources in over a decade of war. Some time by the year 0 BBY, the criminal Jyn Erso spent time bouncing around the Mid Rim on planets such as Coyerti and Cerea before settling on the planet Takodana for almost a year.
In 3 ABY, during the Galactic Civil War between the Empire and the Rebel Alliance, the Coyerti entered their reproductive season, which left the natives defenseless against the Empire's forces on Coyerti. As a result, a message was sent to the Alliance High Command of the matter. Three weeks later, the High Command sent the Alliance's 61st Mobile Infantry, better known as Twilight Company, to Coyerti to protect the planet's natives. The deployment came with additional goals, one being to provide cover for the Alliance's forces that were withdrawing from the Mid Rim following a failed campaign. The second was to test knowledge provided by the defecting Imperial Governor Everi Chalis on the Distillery.
Twilight Company deployed squads of rebel soldiers onto Coyerti using dropships. On the first day of the campaign, two squads—led by First Sergeant Hazram Namir and Sergeant Zab respectively—attacked an Imperial scout post that was being used as logistical aid in the Empire's offensive against the Coyerti natives. The two squads overran the Imperial camp within ten minutes before rigging its equipment for detonation and escaping into the jungle before TIE/sa bomber reinforcements could arrive.
On the second day, Namir's squad prepared to ambush an enemy convoy, only to find out later that the Imperials had changed course. The same day, the first large-scale engagement occurred when a dozen Twilight squads led by squad commander Carver attacked an Imperial fort. As the night passed, the battle came to an end, with the rebels coming out victorious. The next day, Namir and his squad were tasked with destroying an Imperial AT-ST walker. The four rebels made hit and run attacks on the walker, but later changed tactic and led the AT-ST into a marsh, where the vehicle sunk into a bog.
On the fourth day of the Coyerti campaign, Namir's squad travelled from the bog and into Coyerti's highland jungle enroute to the Imperial Distillery, using intelligence provided by Chalis. Stopping to eat at sunset, the squad travelled until midnight before getting some rest. The next day, they stalked the Distillery and observed the patrol patterns and entry points. When a lightly armored transport arrived around midday, the rebel soldier Brand used the opportunity to sneak into the compound and plant a microdetonator at the bottom of a blue chemical barrel, set for thirty minutes.
When the detonator set off, releasing the barrel's toxins, the Distillery began an evacuation, with all of its entrances opening up for personnel to make their way out. Namir's squad sneaked to a back entrance and killed its sole stormtrooper guard before making their way in and planting explosives in various rooms, killing an Imperial laborer who had failed to evacuate. Once done with their task, they escaped from the Distillery and made it half a kilometer before the explosives destroyed the compound completely.
In 4 ABY, in a conversation on the swamp planet Dagobah, the Force ghost of the Jedi Obi-Wan Kenobi told the aspiring Jedi Luke Skywalker that the fate of Coyerti and many other planets depended on a final confrontation between Skywalker and the Sith Lord Darth Vader.
Coyerti first appeared in the 2015 novel Battlefront: Twilight Company, written by Alexander Freed.