398 was a human stormtrooper who served in the First Order. They were one of the many troopers stationed on the Colossus refueling station, and accompanied Sergeant CS-812 to chase down CS-515, who Commander Pyre believed to have erratic programming. In reality, it was Resistance spy Kazuda Xiono wearing CS-515's armor after the trooper had been knocked unconscious. Xiono managed to escape and put the armor back onto CS-515, who was tracked down by 398 and taken away for reconditioning.