Fsir was a Watith captain who captained the freighter Saltbarrel. In 18 BBY, the Grysk operative known as "Jixtus" hired the captain to attack the Chiss heavy cruiser Springhawk to prevent its commander, Senior Captain Thrawn, from stopping a plot to cause a civil war in the Chiss Ascendancy nation.
While the Springhawk traveled the Unknown Regions in search of the Vagaari pirates, the Watith began a skirmish between Fsir's freighter and its complement of remotely-controlled Watith gunboats, bringing the Chiss cruiser out of hyperspace during the engagement. After the gunboats attacked his flagship, Thrawn destroyed the warships and "saved" the Watith, and Fsir offered to bring him to the nearby "Vagaari pirate base" to express his gratitude. Once they arrived at the base, the Watith sprung a trap: the gunboats attacked the Springhawk; however, the Chiss disabled the Watith starships and captured Fsir.
Fsir was the captain of the Saltbarrel, a freighter equipped with a complement of gunboats and a gravity well projector. In 18 BBY, a Grysk operative known as "Jixtus" hired Fsir to attack the Chiss heavy cruiser Springhawk, giving the captain the region he would be searching and telling him to keep the heavy cruiser occupied, as Jixtus sought to prevent the Chiss Senior Captain Mitth'raw'nuruodo (Thrawn) from foiling a Grysk plot to instigate a civil war in the Chiss Ascendancy nation.
While the Springhawk searched for a remnant of the Vagaari pirates gang, the Saltbarrel used its gravity well projector to bring the vessel out of hyperspace as the Watith freighter and three of its gunboats engaged each other in a staged battle. Fsir called the Springhawk, asking for assistance in his battle against the gunboats, which the captain classified as "evil marauders." When Thrawn refused to assist as he was on a "vital mission", a Watith gunboat was ordered to attack the Springhawk. The other two gunboats were also dispatched to attack, but all three were destroyed. Fsir then thanked the senior captain for his assistance, telling Thrawn the name of his people, where they came from, a system far away, and that his leaders had tasked him and his crew with searching for a suitable location to put a long-range triad transmitter. After Thrawn revealed that he was looking for the Vagaari, Fsir offered to guide him to a local Vagaari base, an offer Thrawn accepted with the condition of waiting until his crew studied the gunboats' wreckage. The senior captain and four warriors would twice board the Saltbarrel to meet Fsir's crew and technicians.
After days of analyzing the gunboat wreckage, Thrawn was led by Fsir to the alleged Vagaari pirate base. After they arrived at a planet that Fsir claimed to house the base, the Chiss and Watith vessels faced twenty gunboats remotely piloted by Fsir's crew. As the gunboats attacked the newcomers, two of them broke off and moved to the other side of the planet; the Watith captain claimed that they were traveling to the Vagaari base, an orbiting weapons platform on the far side of the planet, characterizing the platform as "horribly powerful and dangerous." The captain warned that if Thrawn did not stop the gunboats, neither the Chiss nor the Watith would ever see another moonrise. However, he did not fool the senior captain, who knew that the Watith was trying to deceive him. As the gunboats moved to attack the Springhawk, Thrawn fired spectrum lasers at the pair of lead gunboats, creating a cloud of debris smoke. The Springhawk would then fire a salvo of plasma spheres at the gunboats. However, because the Watith freighter saw the launching of the spheres, the gunboats were mostly able to get out of the way. This indicated to the Chiss that the gunboats were being remotely controlled, because they would not have been able to see the plasma spheres being launched through the cloud of smoke. After the Chiss heavy cruiser Grayshrike arrived at the site of the battle, instructing the gunboats to surrender, the Saltbarrel attempted to flee; however, Thrawn disabled the freighter with plasma spheres, sending a boarding party to the vessel to disable its remote piloting systems. Afterward, the senior captain interrogated Fsir, who told him that an "unknown alien robed and hooded with a veil" hired him to attack the Springhawk.
Shortly after, Thrawn studied the Saltbarrel, convincing himself that Jixtus had hired Fsir at the Unknown Regions planet Zyzek. At Zyzek, Thrawn confronted the Kilji Generalirius Nakirre, Jixtus's ally, who offered to take the Watith to their home although he did not know where it was located; however, Thrawn declined the Kilji's offer.
Fsir was hesitant when Thrawn asked him to identify his people and tell him where they came from, classifying these questions as unsafe and considering Thrawn's query on the Watith's purpose safe. He believed that if the "evil marauders" had captured him and his crew, they would have been sorely disappointed by their "banquet" of specialized electronic equipment and their lack of marketable goods. Fsir claimed that his encounter with the Chiss was remarkable and that the universe had decided to reward Thrawn for his courage and kindness to the Watith; however, he feared that the Chiss sought to join the Vagaari pirates, being unconvinced by Thrawn's statement of the contrary.
After the senior captain remarked that he would have to study the gunboats' wreckage, Fsir asked if the Chiss was blind, calling him and his people wizards after learning that they could learn much about the vessels' crew by studying the gunboats. He was weary about Thrawn's visit to the Saltbarrel. After Thrawn stated that there was no Vagaari pirate base in the system where he defeated Fsir, the captain called him a fool.
Fsir appeared in the 2021 novel Thrawn Ascendancy: Greater Good, the second volume in the Star Wars: The Ascendancy Trilogy written by Timothy Zahn.