During the Imperial Civil War, an assault was launched against the Emperor's Royal Guard on the planet Yinchorr. This event transpired following the obliteration of Byss, the Sith world where the throne was located, and the ultimate demise of Emperor Palpatine. Carnor Jax, a member of the Emperor's Royal Guard with aspirations of becoming a Sith Lord, was complicit in the Emperor's downfall, an act designed to pave his way to claiming the Imperial throne.
Jax's rogue faction then initiated a purge within the Empire, targeting those loyal to Palpatine. This led to a violent attack on the Imperial Royal Guard Academy situated on Yinchorr, with the objective of eliminating the remaining Royal Guard members. These guards possessed knowledge of Jax's treachery and sought to avenge their Emperor. The resulting carnage claimed the lives of 18 guardsmen, including their commander, Ved Kennede. Only one guardsman, Kir Kanos, survived the onslaught, vowing to uphold the guard's oath to assassinate Jax and exact vengeance for Palpatine.
After Emperor Palpatine's initial death during the Battle of Endor in 4 ABY, his Royal Guardsmen were dispersed until they regrouped on Byss in 11 ABY, following their master's resurrection in a cloned body. After Palpatine's final death on Onderon that same year, many of his Royal Guardsmen also died in the destruction of Byss, caused by a malfunction of the Emperor's Galaxy Gun superweapon. Additional members perished during the destruction of the Emperor's flagship, the Eclipse II. The few remaining survivors journeyed to the Imperial Royal Guard Academy on Yinchorr.
Ten days subsequent to Palpatine's demise, a wounded survivor arrived at the Academy: one of the two guards who had accompanied Palpatine to Onderon. He had been injured and presumed dead by the aspiring Jedi Rayf Ysanna, but had, in reality, survived. By eavesdropping on the New Republic interrogation of the Emperor's physician the surviving Guardsman discovered that Palpatine's clones had been sabotaged by poisoning—and that Carnor Jax, a Royal Guard member who had not returned to Yinchorr with the others, had ordered the poisoning. The assembled Guardsmen pledged to relentlessly pursue and eliminate the traitor, avenging Palpatine's death.
Simultaneously, a large number of Imperial stormtroopers dispatched by Jax invaded the Academy, forcing the Guardsmen to defend themselves. Vastly outnumbered, exceeding ten to one, they were gradually overwhelmed, even losing their instructor Ved Kennede, until only Kir Kanos and Kile Hannad remained. They decided that one of them would sacrifice himself so that the other could live to fulfill the blood oath against Jax, they flipped a coin. The coin toss determined that Kanos would be the one to hunt down and kill Jax, leaving Kile Hannad to die a warrior's death. While Hannad engaged the remaining Imperial forces, Kanos stealthily left the Academy before it was destroyed, escaping from Yinchorr to the portworld Phaeda as Hannad enjoyed a warrior's death.
Jax later discovered from an analysis of the dead that Kanos had escaped, and ordered his forces under General Redd Wessel to continue searching for the last individual who knew the secret of how Jax had seized the Imperial throne. Jax regarded Kanos as a significant obstacle to his plans for Galactic domination, and potentially the only person in the galaxy capable of reversing his actions.
Following the massacre, Kanos maintained a low profile on Phaeda for some time, where he inadvertently became involved in the conflict between the New Republic and the Galactic Empire. His involvement would ultimately aid him in fulfilling the blood pact against Jax, finally killing him in The Squall on Yinchorr.
The massacre of the Royal Guardsmen on Yinchorr was initially portrayed in the third issue of the Dark Horse Comics mini-series Star Wars: Crimson Empire. This event serves as the primary catalyst for the conflict between Kir Kanos, the series's protagonistic anti-hero, and Carnor Jax, the series's antagonist.