I'm going to start a Pokemon fanfic where the main trainer, a girl named Idunn after the Fire Emblem character, was raised by a Zoroark who gets captured, sparking Idunn to try and save it. My issue is that she would be incredibly hard to write, as you could guess. And, not to mention, she would be a thief who uses her 'brother', a Zorua, to steal. I don't know where to start with her, honestly.
Besides what gimmepie has already mentioned: hopefully she does not end up becoming a sort of Plasmoid.
The main hurdle in writing characters with a relationship to authority and to their world as you see in Idunn, IMO, is that unless you make them the "stereotypical" rebel who is going through a phase or who simply "knows" what Pokémon Training Anarchism means because they read a few memes (not even the in-universe Wikipedia page on the subject) it's quite difficult to ground them in a strong enough truth that their relatability won't break from the world around them. You have to build them up on a foundational lie, say for example "Pokémon Training is bad because old people tell everyone else what to do" then make the work to twist the lie ("the old people are precisely retired Trainers who grew up with both education and real world experience, so better them than some paper pusher").
So if you have this person who could be "very staunch in her beliefs/dislike of her system", has built up this personality from a narrative lie, then the perfect quirks and hobbies to add to her characterization would be something like visiting parks, libraries and museums.
Not only are things like museums usually free or near-free access to information (breaking the barrier of "power dictates knowledge") but also you could give it a spin to it where it is part of an unconscious mental process on her part to try and understand why "power" works that way - after all, what else do libraries and
in particular museums are but ostentatious public flexes of your power to simply
hold something of importance and not only do nothing (evil) with it but at the same time flaunt that nothing is expected to happen to it, unlike a Pokémon fight where I imagine at least in competitive circles, injury is a given?
My character, Faye, in Guild's of Atria is actually a tiny bit hard to write out. She's the quiet type and shows her kindness and goodwill through actions rather than words. She's also an emotional mess and can't tell how she's feeling. It makes it harder to write out certain situations that depend heavily on emotions. It's a challenge sometimes.
Can not speak much for everyone else in the world, but from my understanding people who "can't tell how they are feeling" is because they lack the richness of interpersonal experience to see their behaviour reflected on other people, who then give it names. It seems to fit well with her means to communicating emotionally with other people is mostly via action, perhaps never stopping to ask "are you ok?" but rather
assuming that people are ok, or
assuming that people need help.
I could see such kind of character growing a "Poisonous Messiah" Syndrome ("you HAVE to be hurt! And if you are not, I'm going to make SURE that you are, because if you are not hurt you can not be SAVED").
As for myself, honestly the only thing I'm writing right now is
Sabres in the Sandstone, and since 85% of the cast there literally is not mine I'm kinda forced to say that the most difficult character I'm writing at the moment is the Cadrícean Cobalion. Writing a quadruped is already hard when it comes to combat, and having to write a character that is so different to the Cobalion that I think most fans relate to (the one in the Keldeo movie) can put one at odds with potential readers; but writing his personality and mannerisms is also difficult because he lives a special duality: he wants to remain in obscurity, he shuns the spotlight, but at the same time he wants to remain informed and he wants to gain an insight of "the bigger picture". And because he's so isolated from half of the world (the human world) even if he tries, he does not even know what compromises can he make - the closest he can get is, well, challenging Trainers to ssee what do they show him.