Think of Luthen like a really stern coach on a sports team. He knows Cassian and Bix are potentially two of his best players, but he also knows they can play at a higher level than they have been recently. The coach yells at and pushes them harder and harder, to the point where the players think the coach doesn’t like them. But then, come game time, he puts them in.

It was an important mission. We heard Paratgaz tell Loni that he (Partagaz) was being forced to give up the interrogator to the wider Empire because he’s been so successful. The Empire was about to implement his torture regime as standard policy. Loni passed the intel on to Luthen because that guy needed to get got. Luthen chose to give the mission to Cassian and Bix because he knew they could get the job done right, but also because he knew that it would be a better salve for Bix’s trauma than the drugs she was using.

Luthen needs Cassian, and Cassian needs Bix. “You want my blood? You help me figure this out.”