I got this prince in medieval times who is someone who is into the creative arts but because of that, they are not seen as a good fit for a king. Then when they get part of their dad's kingdom because the king dies unexpectantly and he didn't have a clear heir the kingdom is split between all his children and this prince is basically sent to his "death" when they give him this forest where these murderous shadow creatures called banes live. They currently have no known way of being killed so he basically just runs and hides. So my question is, should he be a vengeful force over time or....
Great characters write their own stories. I agree with big soft moose -- write the tale. It might lead you somewhere unexpected. You own relationship with the character and the character's relationships with other characters will grow and develop with time. It may not be as black-and-white as you think.
Yeah, I'd be vengeful. Or at least very irritated. In this case, I would wonder what kind of political entity would have the power to divide a kingdom into five pieces, unless it was a consensus among the children themselves. Or if such an entity had the power to do that (like an army), why they wouldn't just take the kingdom for themselves.
Yeah, I agree with those who have said, basically, write the book and see where it takes you. If you try to get people to validate your ideas or to generate them for you (yikes) you will end up writing somebody else's story, not your own. Do you have a notion, at the moment, where you would like this story to go? Besides being artistically inclined, what is your character actually like? Is he moody and introverted? Is he the sort who sees beauty wherever he goes? Is he well-liked by other people? Does he have friends? Allies? Is he the sort of person who is meticulous and careful with his craft, or does he just create in a flurry of inspiration? How does he feel about being banished (never mind the 'banes.') Is he secretly relieved that he doesn't have to be king after all? (And if this is the case, what would make him change his mind ...IF he changes his mind.) Or is he angry that the position has been taken from him? Or is he confused, because he never really thought it through, but always 'expected' to be king? Is he sad because his father has died? What (besides not getting injured or killed) does he actually want? Will this 'want' change as the story progresses? What sorts of skills does he have? What is his attitude toward learning new ones? Has he ever had to face trouble before? What do you think a person with his character and personality is likely to do, in the circumstances he finds himself? Will he just sit passively, waiting for something to happen or for somebody to rescue him? Or will he take steps to sort the situation? Do YOU think he would make a good king? Why or why not? And etc. I stress that I don't need to know the answers here on this thread, and don't expect you to answer them here. This is YOUR story. But these are the kinds of issues you might want to be thinking about as you build your story. Because, as @A. P. Land pointed out, your story will evolve as you write the character, and see how he interacts with the other characters and his environment. Let that happen, and follow your instincts! It's one of the most enjoyable aspects of writing fiction, in my opinion. Don't get hamstrung by the common 'new author' fear of 'wasting time writing stuff you're going to have to delete, etc.' Expecting to get the story perfect before you start writing is one of the commonest misconceptions inexperienced writers have. The important thing is to get actually writing. Yes, you will end up discarding some of what you write and rewriting lots of it. But that's not time wasted at all. This is how you learn. There aren't any other occupations or skills I can think of, where a person must achieve perfection at the first go, or they are failures forever. Making mistakes and finding ways to correct them or work around them is part of the learning process—and is a risk-free process, for a writer. So is solving your own story problems, on your own. If you wait for perfection to strike, you'll probably never get started. And if you need other people to input their ideas and critique yours before you can start, you'll be writing with the brakes on. So ...get started! And make this YOUR story. If it ends up being a 'vengeful' story, then that's fine. It may end up being something else. But as long as it's true to your character, it will feel right. Good luck!
The Netflix show El Cid has this plot, a king dies and splits his kingdom amongst his three sons and two daughters. It sounds like your MC got the worst of the deal, rulership of an untamed territory full of monsters. From this beginning, however, he can rise to great heights. Defeating monsters will make him brave and strong, and he will attract followers under his banner. Eventually, he will have an army strong enough to challenge his brothers and sisters, and conquer them and become king of the entire kingdom. Assuming, that's where you want the story to go.