During the High Republic Era, a male human named Dass Leffbruk lived, the son of Spence Leffbruk, a hyperspace prospector. Eager to participate in adventures, Dass went with his father on his journeys. He and his father were once marooned on the planet Gloam after a trip to the paradise planet known as Planet X; however, Jedi Master Silandra Sho and her Pathfinder team rescued them. Later, Dass, along with his friend Sky Graf and Nitani, attempted to locate Planet X again using a Graf compass, but ultimately gave up.
Leffbruk was the child of his father and mother, spending his early life traversing the galaxy. Following the loss of his mother in a shuttle accident during his infancy, he continued exploring with his father aboard their vessel, the Silverstreak. Throughout the Eiram and E'ronoh War, Dass and his father faced numerous dangers, including being caught in a blockade, detained by security personnel, and pursued by pirates exploiting the conflict to prey on vulnerable ships.
Around 382 BBY, the Leffbruks joined forces with Radicaz "Sunshine" Dobbs, another prospector, in search of a paradise planet.
Ultimately, Dobbs abandoned them on the planet Gloam. Spence sustained an injury while trying to detach a piece of hull plating from wreckage, necessitating his stay at their camp. Meanwhile, Dass independently ventured out to hunt for sustenance, all while evading the monsters that roamed the planet. He would head in a direction to survey the terrain and capture scrabblers for food. He investigated the ruins of an old city. Growing anxious, he made his way back to their campsite. Spence was happy at his son's return, and apologized for stranding them on the planet. Dass brushed off his father's apology and examined the makeshift emergency beacon he was trying to put together. As darkness descended, they sought refuge inside a cave they had established as shelter. Dass persisted in his exploration and hunting endeavors, returning to camp after an unsuccessful outing. Exhausted, he lingered outside the cave, only to realize the creatures had altered their tactics, arriving earlier under the cover of an approaching storm. He and his father sought refuge in their cave, barricading the entrance with a metal plate. A monster breached the barricade and seized Dass, but Spence repelled it by stabbing it with an improvised weapon. Dass realized that their distress beacon was vulnerable, situated outside the cave.
After remaining awake throughout the night, Dass stealthily ventured outside to retrieve the beacon, only to be ambushed by a monster. He jabbed it with the prod, but failed to deter it. The young man was rescued when his father hurled a rock at the monster, inflicting injury. Once safely back in their cave, Dass revealed that the beacon remained intact.
Shortly thereafter, Dass was present when Mittik and Dietrix Jago responded to their distress signal and located their cave. Initially wary, he and his father warmed up to the strangers, who provided them with sustenance and medical attention while the Leffbruks recounted their journey to a paradise planet and subsequent betrayal by Sunshine Dobbs. Dass shared with Mittik and Jago the joy he felt while on the planet. When Dass mentioned his visit to the ancient city, he offered to guide the group there so Jago could continue searching for the missing Pathfinder team.
Upon reaching the ancient city, Dass grew apprehensive about entering. Jago suggested that the Leffbruks could wait outside, but the boy, not wanting to risk being stranded on Gloam again, decided it was best to remain together. Dass assisted Jago in hotwiring an old pneumatic crane to access one of the entrances, amused by the pilot's enthusiasm. Once the crane was operational, he entered the basket and was lifted to an archway leading into the city. Looking down, he felt nauseous due to the height and gripped the basket's railing. Overcoming his fear, Dass jumped onto the ledge and joined the group to explore the city. As they ventured deeper, Dass and the others discovered tapestries depicting the history of the Katikoot people. Descending further into the city, the party encountered a large swarm of monsters emerging from a central pit. Dass seized Spence's prod and used it to fend off several creatures attempting to attack them. When a monster grabbed the prod and tried to drag him over the pit's edge, Dass released it, sending the monster tumbling down. He and the others quickly retreated into a small alcove to escape the swarm.
Trapped in the alcove, Dass embraced his father, expressing gratitude for taking him on his exploration of the Galaxy. He confided in him his desire to join a Pathfinder team if they survived. Before the monsters could reach him, the Jedi arrived and engaged them. Rooper Nitani introduced herself to the Leffbruks and instructed them to prepare to run once the Jedi had cleared a path to the city's exterior. Once the path was clear, Dass sprinted with the others towards the Pathfinder's ship parked outside the city. Upon reaching the Umberfall, Dass and the others were horrified to witness Rillik's transformation due to the miner's curse and quickly boarded the ship. The boy managed to escape Gloam with the Pathfinders and Jedi, finding safety on Aubadas.
Several days later, Dass and Nitani sat by a waterfall in Diurna, discussing their future plans. The Leffbruks would accompany the Pathfinder team to Batuu, where Dass and his father would attempt to recover their ship. He joined the celebration that erupted upon the announcement of a ceasefire in the Eiram and E'ronoh War.
On Batuu, Dass was approached by his friend Sky Graf of the Graf family, who sought their assistance in locating the mysterious paradise planet known as Planet X. Dass hoped to retrieve recordings of his mother from the Silverstreak there, while Graf hoped to find their father, who had crashed there, still alive. Their plan involved using a special compass possessed by Graf, capable of directing them to a desired location if they had an item from that place. Graf hoped that Dass himself, having been to the planet, along with Nitani's assistance with the Force, could make the compass function. They also participated in an event called the Hyperspace Chase to conceal their intentions from both Graf's family and Spence. However, they eventually chose to abandon their mission to help save lives during the Night of Sorrow, a conflict between the Jedi and the Path of the Open Hand, by restoring communications over Dalna, the planet where the battle was taking place. Dass and Graf also moved on from their initial motivations for wanting to reach the planet, and both decided against continuing the search.