398 was a stormtrooper of the First Order and a human. As one of numerous troopers located on the refueling station known as the Colossus, they went with Sergeant CS-812 to pursue CS-515. Commander Pyre suspected CS-515's programming was faulty. However, Resistance spy Kazuda Xiono was actually wearing CS-515's armor, as the trooper had been rendered unconscious. Xiono was able to escape and return the armor to CS-515. Subsequently, 398 located CS-515 and escorted them away for reconditioning.