I had a thought about Harald. When it was first seen, I was very curious how a Abyss mark was in his throne room. Also, Sommers seeing schools and libraries and saying Harald "messed up" also sounded odd.
Now that we know there are ranks to the HK and Harald was one, I think I may have a better guess of what happened.
I think the day he died, Harald was going to be promoted from at least Shallow to Deep, but someone (a Gorosei?) saw his works and ordered Harald to dismantle those institutions, bur he refused. So his mark DR'd him so he would be forced to do it himself. But Loki killed him before he could do so.