Yeah, I don't agree with the "night time prince is still the prince, just unhindered" theory people were trying to push.
It's moreso like a version of him that is warped and controlled by the demons trying to pass through him via the gate. He obviously cares for his people and those around him. It's why he does his best to keep himself locked up at night away from everyone else.
The only reason why the prince himself believes that the night version is still him is due to everyone spreading rumors about him going insane. It's just his spirit, body and mind being distorted by demonic energies causing him to be more unhinged. It's not like he's a psychotic rapist that beats the shit out of people like a sadistic beast.
Oh? That’s what I’m thinking all this time
Do people think he exchanged body with demon or what at night?
The people in the story that don't know he was cursed just think he's ill or going insane.
What's really happening tho is that the demon gate is opening wider each night which is causing his spirit and mind to become warped. It's literally eating away at his soul every night. It's not really him nor is it some sort of hidden version of himself like readers keep implying. We know this 'cause during his moments of clarity at night he regains some control of himself even if it's not enough to stop himself completely.
The same thing is sorta happening with Myungha too. The hex on his back is causing him to have uncontrollable fits at night. Some nights it's just a fever and others have him actively seeking out the prince even if he doesn't understand why.
It's best to see it as a form of possession rather than these characters just basically having a split personality lol
Someone mentioned in the comments earlier that the personality at night is still his highness, just without inhibitions.
My theory is that he's the literal gate to a demon. I remember in the Kane Chronicles by Rick Riodran, Gods lived within mortals and sswitched places or took over when necessary
Foe one character, a God and human even chose to essentially combine. Is that not the case here?