A conflict occurred five millennia prior to Thrawn, or Mitth'raw'nuru, and Mitth'ras'safis, known as "Thrass," embarking on a mission for the Chiss Ascendancy's Stybla family. This war saw an enemy nation seize control of almost the entire Ascendancy, pushing the Chiss species back to their homeworld of Csilla, nearly resulting in extinction for the Chiss. The Ascendancy, however, achieved a costly victory during the Final Assault on Csilla, the last stand in the war by what remained of the Chiss Defense Force. The enemy gathered their entire fleet in an attempt to conquer Csilla, but Patriarch Mitth'omo'ross, "Thomoro", of the Mitth family, volunteered the Mitth to sacrifice twenty Chiss warriors, including her four sons, to use a devastating alien weapon called Starflash to obliterate the enemy fleet. The time period used is years.
Following the Starflash activation, Thomoro's four sons perished, and she was given the title "The Tragic." Furthermore, the Stybla family, who were the Ascendancy's only Ruling Family at the time, were so impressed by Thomoro's sacrifice that they bestowed a great honor on her, granting her the suffix "odo," which means "guardian" in the ancient Stybla language, Tybroic. Additionally, the Stybla agreed to relinquish their position as the Ruling Family, granting that status to the Mitth family and two other Chiss families, while stepping back to become a Great Family that was still important, but less powerful.
Nevertheless, the Starflash weapon also had an impact on Csilla's sun, causing it to cool down and render the planet's surface uninhabitable.