From what we can tell he seems to want to destroy the empire fl ex is rulling and he is using trashta to do it.
Spoilers
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From what I remember (it's really vague in my memory) he wanted to take revenge on Sovieshu.
When he was younger, Sovieshu managed to trick one of his father's mistresses/concubines and she was sent away. Then this woman married Duke Ergy's father and basically messed up his family. So for Ergy, Sovieshu is responsible for his family's misery because if he had not helped chasing this woman out of the palace she wouldn't have come to know Ergy's dad and his family wouldn't have been destroyed.
Not exactly sure too, it's just what I remember the spoiler said so don't believe me 100%
Thanks for the answers! The spoiler from Yona6 surprised me but also made sense somehow. Cause duke Ergy seems to really have a specific person in mind for wanting to ruin the empire (that Sovieshu is ruling).
Does anyone know Duke Ergy's goal?
At first I thought he just went with the flow, then I thought he liked Rashta but it doesn't seem to be the case... He seems to have a goal in mind but I can't seem to grasp it. Also it doesn't help that I haven't seen the beginning of this story for quite a while now (when I rewatch the story I start from the divorce and after) so I might have known his game if I saw it from the beginning but I don't like the drama...