Arjin was a Trill initiate for the symbiosis program. Arjin was qualified as a Level 5 pilot, and a specialist in astrophysics (i.e., an astrophysicist). His father had been a pilot instructor at the Gedana post for forty years, but died in 2369. He also had a sister.
In 2370, he traveled to Deep Space 9 on board the USS Nash for instruction and evaluation by his assigned field docent, Jadzia Dax. He was very nervous about meeting her, because he had heard how difficult Curzon Dax was with initiates, and Jadzia carried the Dax symbiont. When he did meet her, he was surprised how easy-going and full of life Jadzia was.
Arjin was intelligent and skilled, especially as a pilot. Dax questioned his motives for joining with a symbiont. Dax believed Arjin had pursued joining because it was expected of him and she did not believe he had given enough consideration to his own wants and needs. Because of this she was concerned that his own personality and identity might be overwhelmed by the symbiont. This would prevent both Arjin and the symbiont from achieving 'the next level' for a joined Trill. Dax told him how shy Jadzia herself had been, but had still made it through the selection program despite Curzon. She told Arjin that he needed to find an inner strength and assert himself. She encouraged him to return to Trill and re-evaluate his priorities before fully committing himself to such a life-altering decision as joining.
While on a trip to the Gamma Quadrant, Jadzia and Arjin accidentally brought a protouniverse back to the station. It was expanding and threatened to destroy the Alpha Quadrant. Commander Benjamin Sisko ordered it returned to subspace in the Gamma Quadrant. Dax invited Arjin to pilot the Runabout with her, and he agreed. Inside the wormhole, Dax ordered Arjin – an expert pilot – to navigate through a minefield of nodes. Arjin was at first reluctant to do so, not trusting his pilot skills. The protouniverse's containment field then collapsed, leaving no margin for error, but Arjin succeeded in getting them through the wormhole, returning the developing universe to its subspace pocket. He won Jadiza's respect both in the way he handled the crisis and standing up for himself. As a result, she recommended him for joining to the symbiont commission. (DS9: "Playing God")