I suspect the entire arc will be about Loki .
So Harald has Ancient Giant blood race and he cut off the horn to show he no longer associates with them .
I suspect Harald was ashamed or hates his bloodline and there is note of Loki and Jarul surviving this incident .
whatever happens Jarl knows about the Harald’s assassination . He is definitely hiding something we don’t know yet ? Did Loki actually kill Harald or there was conspiracy involved .
I think it's all set up to easily come around to Loki's belief that he'll destroy the world, those Harley texts mentioned last chapter, and the Nika prophesies.
The royal family of Elbaf has a legendary DF thought to be linked to the Sun God.
The Harley text mention that Sung God Nika has ended the world twice already, and will do so a third time in the future.
The folk tales on Elbaf speak of the Ancient Giants as bloodlust beings, ravaging everything in their path, and in fact being moved by such bloodlust as to be able to destroy the whole world if left unchecked.
Therefore, Harald thinks someone with Ancient Giant blood (signified by the horns) and with the Sun God DF will end the world.
So he breaks off his own horns, rejecting the legacy imposed on him, and hides the DF away.
Then he is assassinated.
Loki has the same horns as the Ancient Giants, and when he comes to own the DF (either voluntarily or not, we still don't know), he inherits his father's belief that he will end the world--only Loki isn't worried about it, he instead embraces this prophecy.
The twist I expect is however threefold.
Not only
isn't Loki's DF the Nika fruit.
Not only will Nika end the world for
good reasons.
But Luffy himself will be revealed to have Ancient Giant blood--
without the horns, just like Hajrudin.