Imagination. Writers are required to utilize it, to bring a unique spin on familiar themes. But what happens when readers, who heretofore demanded originality, cry, "You can't do that!"?
I'm not referring to obvious situations where an action results in a specific reaction. For example, if an ordinary person is shot, he or she will bleed. Now if the person has preternatural abilities then the game plan can change.
What I'm talking about are certain characters, particularly supernatural ones, whose actions have become defined by a set of unwritten rules.
Take the vampire for example. He or she is repelled by garlic, shuns holy water and crosses, turns into dust in sunlight, and is generally evil. A simple basic formula every writer crafting a vampire story should adhere to, right?
Um, yeah. Whatever. If that's true, then how does Miyu, the titular vampire from Narumi Kakinouchi's manga and anime Vampire Princess Miyu, move through the human world with ease? Holy water and crosses have no effect on her. She walks in daylight without fear.
Hellsing's Alucard uses bullets made from the silver of a melted cross. Unlike Miyu, however, he prefers the night. But his agenda is different from hers. He hunts other vampires. Miyu targets Shinma, god-demons who escaped when the gate between their world and the human one was opened.
Angels also seem to be forced into certain roles. Here the rules imply holy angels must always be good. Demons and fallen angels must always be evil.
Why? What purpose does it serve to pigeonhole these characters? If your vampire wants to work on the side of justice (Angel, Nick Knight) then let him or her. If your demon desires to fight evil, why say no? If he has free will then it would seem an individual choice. For that matter, why can't a holy angel become corrupted with power?
When we restrict our characters, we essentially shut off that part of ourselves which probably inspired us to write in the first place. We lose that ability to wonder "What if?"
Remember, you're the writer. These are your stories. Just because someone says your character can't do something, doesn't mean they're right. Challenge their preconceived notions. Give them something different.