Character Designs
Characters are essential to stories because of the uniqueness each brings. They are most interesting when they are most realistic. This doesn't mean in terms of their "realness" in our world, because authors like JK Rowling invented beasts that do not actually exist, but still feel very real. By "realistic", I mean in terms of their flaws, their good and bad qualities, their moral compass. One shouldn't be able to tell so easily if a character is "good" or "bad", because everyone is a bit of both in reality.