The plot thickens! It also occurred to me that Aurelia, who Adorie shares colors with, was also called the Twilight's Majesty, so maybe she's the source of the Evening Sky's majesty domain? No idea how that would happen, but everything is possible in the crazy lands of EFB AU.
Edit: Hmm, actually, Aurelia fits Evening Sky's themes really well. Both the insane Cha and the Protection it grants. It misses her excellence, but you can't have everything.
Counter point, who was the Pirate to bear part of the Sky's Mantle?
What was his connection to the Royal Family of this land, that he bore such a relic? What might he have said to us, if give the leave to speak?
With what we now know, I have a theory that answers those questions, in a very Rihaku like way, what if he was Adorie's brother?
It would fit Rihaku's style to have that plot thread dangling in the world, the escaped son of the line, perhaps disgraced, or merely fled, seeking power, allies, or anything really to change what has befallen his people.
We know that mercenaries were hired to kill the Armament, he could well have been one, and given this line.
Once designated, a companion cannot be replaced until they are slain beyond the possibility of recovery; take care that you do not raise up a Mordred or Lancelot.
I have to believe that one of our present companions, or one we may acquire soon, is a hidden threat. I thought it was Aobaru, and it yet may be, but it could just as easily be Adorie who turns on us, perhaps in vengeance, wouldn't that be a familiar twist?
It feels like Rihaku to have our hasty choice come back to harm us, and we struck down the Sky's bearer as he tried to parley, this may be the hidden cost.