Vaylin was a Force-sensitive female Human daughter of Senya Tirall and Valkorion. The younger sister of twin brothers Thexan and Arcann, she displayed incredible potential in the Force since early childhood, but was also difficult to control, causing Valkorion to lock her away on Nathema, fearing that she could one day challenge him. In Nathema’s Sanitarium Vaylin was subjected to intense mental and physical torture that broke her innocence, turning her into a sadistic person with no empathy for others. Senya attempted to get her daughter out, but was stopped from doing so by Valkorion, causing Vaylin to blame her mother for her suffering and develop an intense hatred for her. Subjected to a mental conditioning only Valkorion knew about, Vaylin was eventually allowed to return to Zakuul, where she bided her time instead of immediately striking back. When Arcann arranged for their father’s death, blaming it on the Outlander, Vaylin supported him and became the High Justice to the new Emperor, who conquered both the Sith Empire and the Galactic Republic in less than a year.
Five years into Arcann’s reign, the Outlander was released from imprisonment in carbonite by Lana Beniko and Vaylin personally led the pursuit, but was unable to prevent them from escaping. The fugitives eventually fled the planet on the Gravestone with Senya’s help, giving Vaylin another reason to hate her mother who now fought against her own children. Vaylin fought her mother and revealed to her that Thexan was killed by Arcann. Vaylin personally led a series of reprisal bombardments to lure the Outlander out of hiding and inspected the Gilded Star when Senya assisted the Outlander in raiding the treasury ship while wearing Vaylin’s face as disguise. During the Battle of Odessen Vaylin turned against Arcann, revealing his whereabouts to the Alliance while luring Senya away to confront her mother on her own, though Arcann later returned the favor by stopping Vaylin from landing a blow, after which Senya took him away. Vaylin returned to Zakuul, where SCORPIO has claimed the Eternal Throne in their absence and was surprised when the droid offered the Throne to her, offering to act as Vaylin’s advisor instead.
As the new Eternal Empress, Vaylin led a hunt for Arcann and Senya, confronting her mother on Ord Mantell where she slaughtered a host of Knights of Zakuul loyal to her mother. Tracking them to Voss, Vaylin launched an invasion to draw her family out of hiding, but was unable to kill her family because of GEMINI droids’ newfound self-preservation given to them by SCORPIO. Using the rumors of the Outlander’s death, Vaylin and SCORPIO launched an assault on the Gravestone, taking control of the only vessel capable of fighting the Eternal Fleet. While fighting against an Alliance counter-attack, Vaylin almost killed the Outlander when Valkorion, whose spirit resided in the Outlander’s body, activated her conditioning, making Vaylin aware of it for the first time. SCORPIO took the Gravestone and the Eternal Fleet to Iokath, where Vaylin led her Zakuulan forces to reclaim the Eternal Fleet from ARIES, while also obtaining a way to restore GEMINI to their original programming. Celebrating her accomplishments at the Grand Festival of Empress Vaylin, the Empress was confronted by the Outlander and Arcann, who joined forces to stop her reign. Vaylin returned to Nathema, where the Anomid scientist Jarak responsible for her conditioning helped her break her bounds, after which she immediately launched an Assault on Odessen. During the battle the Outlander taunted Vaylin into a direct confrontation on the surface, in which Vaylin was killed, though Valkorion secretly absorbed her spirit’s strength and enslaved her, and used her power to conquer the Outlander’s mental defenses. As the Outlander fought Valkorion for control of their body, Valkorion sent Vaylin’s enslaved spirit against his opponent, but instead, the Outlander freed Vaylin from Valkorion’s control, using Dramath’s holocron. Vaylin joined the Outlander and the rest of her family in fighting against Valkorion, which resulted in the final death of the Immortal Emperor, allowing Vaylin’s spirit to depart in peace. When Valkorion’s imprint spirit surfaced several years later in an attempt to resurrect himself, within the mind of Jedi Grand Master Satele Shan, Vaylin’s spirit joined forces with the Outlander and everyone else whom Valkorion had manipulated or killed, finally vanquishing the ancient entity once and for all.