Originally named Diap'assik, Dia Passik spent much of her early life as a slave, far from her home planet of Ryloth. Her enslaver possessed a yacht known as the Violet Hem, and Passik spent a considerable amount of time there. She later revealed to her squadron companions that she harbored some resentment towards other Twi'leks for selling her into servitude.
Passik possessed exceptional intelligence and resourcefulness, which she used to persuade mercenary pilots to teach her how to operate starfighters and other spacecraft. After gaining sufficient skill, Passik commandeered a shuttlecraft and, after disabling the shield controls, destroyed the Violet Hem in what became her first experience in combat.
Eventually, she found her way to the territory controlled by the New Republic and joined Wraith Squadron in 7 ABY. She took the place of Falynn Sandskimmer as the Wraiths' vehicle expert, and her knowledge of various criminal syndicates was extensive. During the Wraith's mission to infiltrate Zsinj's operations, Passik adopted the persona of Captain Seku, a pirate leader of the Hawk-bat Independent Space Force, working alongside Kell Tainer, Garik Loran, and Shalla Nelprin. To prove their loyalty, Zsinj demanded that the fake pirates execute Wraith Castin Donn, who had secretly boarded their ship. Passik shot Donn's already-dead body with a blaster, allowing the team to continue their infiltration. Afterward, she was overwhelmed with grief and self-disgust, nearly taking her own life before Garik Loran intervened, convincing her that she had saved his life by doing what she did.
Passik served with distinction in the Wraiths and the task force led by Han Solo throughout the campaign against Zsinj. During her time in the squadron, she developed a romantic relationship with fellow member Garik "Face" Loran and provided support as he dealt with the loss of his close friend Ton Phanan.
She continued to serve in Wraith Squadron during the Yuuzhan Vong War and was still a member at the war's conclusion.
In 44 ABY, Passik married Loran and started a family with him, raising their daughter together. At this point, Passik was a partner in a commercial air-and-space transport service, working as a pilot.
Aaron Allston, the author of X-Wing: Solo Command, mentioned on his website that Passik would likely have left the New Republic after the Zsinj campaign to fight against slavers on Ryloth. However, since this is not confirmed by any canon source, it remains uncertain whether this actually occurred.