Yllen was romantically involved with Magnus, who held the rank of captain aboard the Stardream, a passenger liner. Together, they parented a child known as Amy. Back in 3639 BBY, the Stardream embarked on a journey originating from the planet Ord Mantell. During this time, Magnus, having received a plush orobird intended as a gift for Amy, instructed her to request a cage for it from Yllen. Regrettably, a short time later, specifically a few days after, the Stardream found itself in the midst of a devastating rakghoul plague outbreak. As Magnus fell victim to the infection, his messages to Yllen became more and more garbled and nonsensical.
Yllen's existence was revealed within a Codex entry associated with the Rakghoul Pandemic World Event. This event was introduced to the 2011 BioWare video game titled Star Wars: The Old Republic, specifically through Game Update 1.1, which was released in 2012.