Arrogant aristocrats who walk around with their noses in the air.
Villains. Edgy
Dominant traits, I suppose, but also protective and overly caring. And I love it when the plot actually creates a sense of danger. Like, that's their personality, but they're right about it.
I also love it when a character's true nature is wild and dangerous, but they're too noble and above it all to show it. And this side is obvious from their actions and emotions.
The relationship reaches its peak when he says: "You're not going to sit on that dirty log," and adds, "Put on your gold-embroidered cloak - it's getting cold."
I like it when a character like this is a little comical, a little of a diva. (Rarity from My Little Pony)
He doesn't have to be smart in the sense of being wise, but he is cunning.
And he needs some amusing quirks. Usually this is achieved through excessive perfectionism or some kind of flaw, like poor sense of direction. I love details like that.
I like the idea that "fate" brings two hearts together.
There are hints of some special bond that has formed between them, and now they are connected by something magical.
I often find characters interesting after they've led legions into battle and survived a bloody massacre, to tell the truth.
I guess it annoys me when characters like the ones I described lose their sharp, edgy traits - or when those traits are deliberately toned down and then called a "growth".
He now loves MC, so his wild side should be directed toward external threats. His sharp traits must not be forgotten.
I find kind, good characters interesting when they show a conflicted side. Or just cute and nice. But I usually never really get into them.
Gray characters is interesting, but I can't remember a time when I was interested in gray characters without a villainous backstory to capture my attention.
My root is loving a tsundere but these days i'm leaning towards more of kuudere 
