I honestly don't remember well, for I read it quite some time ago, but if I'm not wrong I think it was because psyche has the divine power which was said to be esclusive of the imperial family, so the crown prince wanted to obtain it. I think it was explained at some point but I don't remember where, sorry
As for medea he first wanted to obtain psyche's power and then have the fl as empress, for she is wise, but he is also angry at her because he can see that she only look at him as an "object", a way to become empress (he know he is kinda looked down by her and realized it on their first meeting)
The emperor wanted a psyche for her power, and he knows that Medea is more intelligent and furious than him , that is why he chose Psyche to be her empress.
And now That emperor can go and eat trash
But i still don't understand why that idiot prince let go of our queen first and then ask her to be the empress again...like what???
And of its for psyche...
Why did he try to kill her for her powers after their engagement announcement... could have done it secretively without anyone knowing, right???