Villainess comes in one night thoroughly out of sorts because her stupid cousin’s decided to make a move on her rights to the souls of their ancestors, and the jerk’s competent enough to actually have a potential chance at getting them, too, like he’d even wear the necklace of jewels they’re trapped in-!!!
The Prince listens patiently to her frustration until she’s finished, then considers for a few minutes.
“Darling, about that banquet your family’s having next fortnight - will your cousin be in attendance?”
“Yes, he’ll be using it to lay the groundwork of his plans. Why?”
“Would it be all right if I popped in for a bit? And was rather more… myself than I usually am around your parents?”
“…I suppose it’d be all right.”
“Wonderful!” (kisses her hand) “Perhaps wear those full-arm gloves your friend got you for the event - the ones that allow you to handle blessed objects without them interfering with your dark powers?”
“Well now I’m just curious. I shall do as you request, beloathed.”
The night of he shows up to the banquet positively radiating charm, good will, and benevolence, decked out in full armor that’s glowing slightly. Oh this? It’s the ancestral trappings of one of his relatives who was a champion of the stellar deities, those who guide ones who have become lost in darkness? He’s not a holy champion himself, but he is a fully-realized warrior of light and family, so he’s permitted to wear it at times. Oh yes, he completed his warrior of light trials when he was eighteen, when on a quest and everything! That’s where he earned his sword - it’s actually a shard of sunlight, you know, not metal. That’s why he’s called Prince of the Sun and Stars sometimes - bit of a grandiose title, really, but the artists and poets enjoy playing with the imagery, and who is he to deny them, especially when Darling is so fond of the stars herself! There’s a lass in one of the kingdom’s villages doing a portrait of the two of them together playing with that motif, actually, and it looks like it’s going to to be absolutely lovely when it’s done-
And he continues to be cheerful, charming, and just the nicest, most polite guy for the time he’s there while also reminding everyone in no uncertain terms that, for as long as the forces of evil have been trying to quash the forces of good, his side has been working at the opposite. And his side tends to win more often. And maybe it would be wise not to pick a fight with Darling because he’d hate to have to do battle with a potential in-law in the path of supporting her family’s traditions regarding people who cross them…
Jerk cousin is thoroughly cowed out of making an attempt at the family-filled jewels, and Villainess’s friends are standing with her off to the side going, “Okay, beginning to see what you see in him now.” Villainess herself is walking around with on safely-gloved hand on his arm as he intimidates the hell out of everyone she knows in order to help her protect what’s hers, swooning a little bit inside the whole time.
(Hers might be more diversely applicable, but Villainess isn’t the only one bringing something to the table in terms of power. Prince is generally more useful for things like getting birds to sing in chorus or making friends with bunnies, but his family does specialize in slaying evil. She may be skilled at facing enemies of all sorts, but he’s prepared specifically for anyone in her home court who might try to backstab her.)