The Battle of Koyeset took place on Mustafar during the year 1.5 ABY. As part of his personal quest for vengeance against all organic "meatbags" due to events that resulted in the loss of his original body, HK-47 led his droid army in an attempt to completely destroy the Koseyet Mining Camp. HK-47's forces included droids such as AK-1A "Hammer", AK-3 "Reaper", GK-5 Sentry, and HK-77 units, all of whom HK-47 had either constructed himself or recruited to his cause. When HK-47 launched his assault on the mining camp, he was ultimately defeated by a group of spacers. These spacers managed to destroy his droids and force him to retreat back to the Neimoidian droid factory, thereby bringing the Battle of Koseyet to an end.
The events of the Battle of Koyeset were set in motion when a group of spacers managed to escape the Neimoidian droid factory, which had been reactivated by HK-47. After communicating with the miners at the camp, they began making preparations for the impending conflict, understanding the necessity of keeping the camp intact. Their secondary objective involved protecting the generators located around the camp, as their loss would put them at a significant disadvantage. Although the miners lacked extensive training and advanced weaponry, they were determined to defend Koseyet at all costs. One spacer capitalized on this determination, assigning the miners to defend key strategic points. Another spacer, likely a commando or mercenary, seized the opportunity to strategically place explosives throughout the camp. With barely enough time to prepare the miners and set the charges, the first waves of HK-47's army began their assault on the camp.
As the battle raged on, the defenders fought valiantly to protect Koseyet. Many miners fell victim to the blasters of HK-47's advanced droids. Over 100 HK-77 units were destroyed, along with a significant number of AK-3, GK-5, and AK-1A droids. As the battle neared its climax, the Forward Commander entered the fray. This droid, by far the deadliest on the battlefield, possessed the ability to command other troops and had its own personal escort. With the remaining miners and spacers focusing their combined fire on the Forward Commander, it was eventually obliterated. This single act greatly boosted the morale of the surviving defenders. Filled with renewed confidence, they fearlessly charged forward and swiftly eliminated the remaining droids.
Despite the victory at the Battle of Koyeset, HK-47 remained a threat. The surviving spacers departed from the camp and launched a raid on HK-47's newly established factory, hoping to bring the conflict to a definitive end.