
The emperor is a total scoundrel. He loves Lady Kathryn. Ok fine. I already hate you slightly... You had a child with her. Fine...Why do love that son the most? Equality man...What did Cayena and Rezef do wrong?(╯°Д °)╯╧╧ Yet you expect filial piety from them. I am with Rezef on killing this bitch. Don't stop us Cayena ヽ(`Д´)ノ

The emperor does gave a reason to hate those two...though it's a BAD reason that mostly boils down to "I hate their mother." Which is a crap reason to give for abusing and neglecting children, but he's not the first emperor in fiction (or real life) to punish children for the sins of the mother--who, you might notice, is no longer in the picture.

The only reason he loves that child the most is because it's the child of the woman he loves. His other marriages were political, no love involved. And the reason why he expects filial piety from Cayena and Rezef is because they are the official candidates for the throne. He doesn't want to hand over the throne to any of them(except the grey haired kid) but he has no choice
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Guys guys guys this is huge. I was reading ch 65 of the novel and apparently spoiler alert. .......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... Rezef is Raphael's brother and not a prince( ̄∇ ̄")

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Can't be certain but the emperor was probably a faithful guy who loved the empress but the betrayal twisted him so much that he couldn't even love his own daughter let alone Rezef who was the fruit of the betrayal. He probably sees the empress and her betrayal whenever he sees them.
However, this does not excuse how terrible he is as a parent. The children were innocent and didn't deserve the treatment they got from the man who was supposed to be their father.
Anyone noticed the translator simping Keith in every panel? ٩(๑❛ᴗ❛๑)۶