The Stelians are a race of Seraphim from the Far Isles, which are located on the opposite side of the world from the Seraph Empire. The Stelians are a powerful race. Scarab was shown to be able to kill someone and read their fates just by touching their invisible strands of life. And Festival could see the future, hence the reason she let herself to Joram.
There was a time when Joram desires for them to ally with his empire. He sent a group of soldiers with his request, but they never returned. Awhile later, a fruit basket mysteriously appears in his room (a room that is supposed to be impenetrable). This fruit basket contains strange, edible orbs; and they believed that they contained the blood of Joram's soldiers. It seems as though the Stelians are more clever and elusive than the seraph emperor thought.