Fsir was a captain of the Watith species, commanding the freighter named Saltbarrel. In the year 18 BBY, the Grysk agent operating under the alias "Jixtus" engaged the captain's services to launch an attack on the Chiss heavy cruiser known as Springhawk. This action was intended to prevent the commander of the Springhawk, Senior Captain Thrawn, from disrupting a scheme aimed at instigating a civil war within the Chiss Ascendancy.
As the Springhawk navigated the Unknown Regions in its search for the Vagaari pirates, the Watith initiated a skirmish involving Fsir's freighter and its contingent of remotely-controlled Watith gunboats. This staged conflict served to draw the Chiss cruiser out of hyperspace during the fabricated engagement. Following the gunboats' assault on his flagship, Thrawn retaliated by destroying the warships and ostensibly "rescuing" the Watith. Subsequently, Fsir extended an offer to guide Thrawn to a nearby "Vagaari pirate base" as a gesture of gratitude. Upon their arrival at the supposed base, the Watith sprung a trap: the gunboats launched a renewed attack on the Springhawk. However, the Chiss forces successfully disabled the Watith starships and apprehended Fsir.

Fsir held the position of captain aboard the Saltbarrel, a freighter that was outfitted with a complement of gunboats and a gravity well projector. In 18 BBY, a Grysk operative known as "Jixtus" enlisted Fsir's services to attack the Chiss heavy cruiser Springhawk. Jixtus provided the captain with the region where the Springhawk would be located and instructed him to keep the heavy cruiser occupied. Jixtus's objective was to prevent Chiss Senior Captain Mitth'raw'nuruodo (Thrawn) from thwarting a Grysk plot designed to incite a civil conflict within the Chiss Ascendancy.
During the Springhawk's search for remnants of the Vagaari pirates organization, the Saltbarrel employed its gravity well projector to force the vessel out of hyperspace. Subsequently, the Watith freighter and three of its gunboats engaged in a staged battle. Fsir contacted the Springhawk, requesting assistance in his supposed struggle against the gunboats, which he characterized as "evil marauders." When Thrawn declined to offer aid, citing a "vital mission," a Watith gunboat was ordered to attack the Springhawk. The remaining two gunboats were also directed to attack, but all three were ultimately destroyed. Fsir then expressed his gratitude to the senior captain for his assistance, revealing his people's name, their origin from a distant system, and that his leaders had tasked him and his crew with identifying a suitable location for the placement of a long-range triad transmitter. After Thrawn disclosed his pursuit of the Vagaari, Fsir offered to guide him to a nearby Vagaari base, an offer Thrawn accepted on the condition of awaiting his crew's analysis of the gunboats' wreckage. The senior captain and four warriors would board the Saltbarrel on two separate occasions to interact with Fsir's crew and technicians.

Following days of analyzing the gunboat wreckage, Thrawn was guided by Fsir to the purported Vagaari pirate base. Upon their arrival at a planet that Fsir claimed housed the base, the Chiss and Watith vessels were confronted by twenty gunboats remotely piloted by Fsir's crew. As the gunboats launched their attack, two of them broke formation and repositioned themselves to the opposite side of the planet. The Watith captain asserted that they were en route to the Vagaari base, an orbiting weapons platform situated on the planet's far side, characterizing the platform as "horribly powerful and dangerous." The captain warned that if Thrawn failed to intercept the gunboats, neither the Chiss nor the Watith would ever witness another moonrise. However, the senior captain remained unconvinced, recognizing the Watith's attempt at deception. As the gunboats maneuvered to attack the Springhawk, Thrawn unleashed spectrum lasers upon the lead pair, creating a cloud of debris and smoke. Subsequently, the Springhawk launched a salvo of plasma spheres at the gunboats. However, due to the Watith freighter's observation of the sphere launch, the gunboats were largely able to evade the projectiles. This observation led the Chiss to deduce that the gunboats were being remotely controlled, as they would not have been able to visually detect the plasma spheres' launch through the smoke cloud. After the Chiss heavy cruiser Grayshrike arrived at the battle scene and instructed the gunboats to surrender, the Saltbarrel attempted to escape. However, Thrawn disabled the freighter with plasma spheres, dispatching a boarding party to the vessel to disable its remote piloting systems. Subsequently, the senior captain interrogated Fsir, who revealed that an "unknown alien, robed, hooded figure with a veil" had hired him to attack the Springhawk.
Shortly thereafter, Thrawn examined the Saltbarrel, concluding that Jixtus had engaged Fsir's services on the Unknown Regions planet Zyzek. At Zyzek, Thrawn confronted Kilji Generalirius Nakirre, an ally of Jixtus, who offered to transport the Watith to their home, despite his lack of knowledge of its location. However, Thrawn declined the Kilji's offer.
Fsir exhibited hesitation when Thrawn requested that he identify his people and disclose their origin, deeming these questions unsafe. Conversely, he regarded Thrawn's inquiry regarding the Watith's purpose as 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 commercially viable goods. Fsir proclaimed that his encounter with the Chiss was remarkable and that the universe had chosen to reward Thrawn for his courage and kindness towards the Watith. However, he harbored fears that the Chiss sought to align themselves with the Vagaari pirates, remaining unconvinced by Thrawn's assertions to the contrary.
After the senior captain mentioned that he would need to analyze the gunboats' wreckage, Fsir questioned whether the Chiss was blind, referring to him and his people as wizards upon learning that they could glean significant information about the vessels' crew through the study of the gunboats. He was apprehensive 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 labeled him a fool.
Fsir made an appearance in the 2021 novel Thrawn Ascendancy: Greater Good, the second installment in the Star Wars: The Ascendancy Trilogy authored by Timothy Zahn.