Tav Breil'lya served as a key assistant to Borsk Fey'lya. However, he lacked the political finesse of Fey'lya. His attempts on New Cov to persuade Garm Bel Iblis to join Fey'lya's group were exposed to the New Republic Provisional Council.
Born on Kothlis, Tav hailed from a distinguished family, a fact he frequently emphasized by wearing his family's crest. He rose to become Council-Aide to Borsk Fey'lya, undertaking various missions for Fey'lya during the Thrawn campaign. A routine task involved traveling to the planet New Cov to engage with Garm Bel Iblis, as part of Fey'lya's ongoing efforts to enlist Bel Iblis.
In 9 ABY, Tav found himself on the planet New Cov. While there, he observed Lando Calrissian and Han Solo, who were seeking evidence of Fey'lya's activities. Han spotted Tav in the crowd and decided to tail him, hoping to uncover his purpose. Unaware of Han's pursuit, Tav proceeded to a warehouse. There, a woman named Irenez, an associate of Bel Iblis, apprehended him. It was at this point that he realized Han was following him. Before Han could intervene, Sena Leikvold Midanyl, another of Bel Iblis's employees, disarmed him. As Sena interrogated Han, Tav identified him as an Imperial spy and infiltrator. Tav advocated for his execution, arguing that his identity and knowledge of the agreement between him and Sena were irrelevant. Before this could happen, Lando Calrissian and Luke Skywalker arrived. When Sena examined Luke's lightsaber as proof of identity, she determined that Han was not a spy. She then invited them to Bel Iblis's secret base. Tav made a final plea to Sena, urging her not to trust them, but she dismissed him and ordered him back to his ship, which he obeyed.
Like all Bothans, Tav enjoyed political maneuvering and power plays. However, in contrast to Borsk Fey'lya, he possessed neither subtlety nor intelligence. This was precisely what Borsk Fey'lya desired, as he preferred his Council-Aide to be a compliant subordinate, not a potential rival. Tav exhibited unwavering loyalty to Fey'lya, maintaining his belief in Fey'lya's eventual success even when circumstances turned against them.