
Tbh I do feel bad for Rezef, his "father" hates him and manipulates him into killing his real dad just so that his biological son can take over afterwards, then we're supposed to be like "omg what" when it turns out he's a bad person with a broken mentality, the unredeemable fuck is the emperor tbh, your wife did you dirty fuck did Rezef do to his crusty dying ass be born. Lowkey gonna relish and laugh at the emperor's death

Kayena made this mistake of pitying Rezef and making excuses for how he is due to it being the Emperor's fault. And thought if she "loved" as a sister and was kind to him he might change. It ended up with her dearest nanny (whom she loved more than her mother) being murdered by him in a disgraceful way. All due to his petty jealousy.
He is a POS and based on who his parents were a bad seed. The Emperor should have just come out and confessed that Rezef wasn't his son and has ZERO claim to the throne but I think he wanted to keep his pride and get revenge.
My point is if the Empress had kept her legs close to that lowlife (Raphaello's father) none of this would have happened. But then again The Emperor would not have made Ethel...
He is actually the only real son of the Emperor. And he was conceived years after the Empress died. He is the only one who has the right to be called a Prince not Rezef.
The Empress cheated on the Emperor with Raphaello's dad - who is an utter bastard. Who despises the Kedrey family (and Raphaello for looking like his mother) but happily allows himself and his family to live off their prestige and wealth like a parasite. Even after his divorce to the duchess, he requested and was bestowed a title from them and a large divorce settlement - which Raphaello finds despicable given that all he does is berate the Kedrey family.
If the Empress was the type of woman to cheat on the Emperor for that kind of man not only was she is a bad person but also a fool.
Rezef was the product of this affair. And when the Emperor found out that the Empress had cuckolded him he had her killed by putting almonds in her food (shes allergic).
Not wanting to face the humiliation of openly admitting his wife not only cheated on him but produced a bastard as a result of that affair. He killed the Empress and made a backstory that Rezef was his "illegitimate" son. Partly to punish the Empress that her son will now be known as a bastard and also this meant he didn't have to officially acknowledge Rezef as the rightful heir.
The reason why Emperor dislikes both Rezef and Kayenna is that they are the Empress's children. Rezef is a horrible person who was born the product of his wife's affair. And Kayenna is the spitting image of her mother who betrayed him. Although, he does have some small sympathy for Karen and since unlike Rezef she is his child.
Unfortunately, the Emperor lets this vendetta consume him to the point he uses Kayenna like a pawn to set up Rezef. And manipulates Rezef into killing his real father. Because ultimately the one who he wants to be his heir is Ethel - his real son. But as far as most people are concerned Rezef is his "older son". Which complicates things.
Especially, as his pride won't allow him to openly reveal Rezef is the product of the late Empress' affair.
Rezef ends up killing the Emperor after he kills his biological father and when he realized what the Emperor wanted all along was for him not be his heir. So he suffocates the Emperor with a pillow.
In the end Kayenna becomes Princess Consort a temporary Empress until her brother Ethel reaches 20 and ascends the throne. Ethel and Olivia end up together. So, Olivia is a future Empress.
The reason Kayenna took the throne away from Rezef in favor of Ethel was due to jealousy he murdered her Nanny. Not only that he had murder set up as a "suicide" which is the most dishonorable way to die in that society. She realises there was no way to "tame" or "redeem" him so took the thing he wanted the most - the throne.
Since the Emperor got sick Rezef is the reason Ethel is treated badly despite being a Prince and his mother has been neglected when it comes to the basic support she usually gets. But she does not complain since she doesn't want to draw attention to herself or her son that could cause them harm.