X = X-rated. In terms of causing trouble, would your character be an X-rated one? (Yes there are the obvious X-rated stories and characters but here I'm thinking of other forms of fiction and how your character would rate within those). Does your character delight in stirring up trouble that would be classed as X-rated by the authorities? And does X-rated carry the same meaning in your fictional world as it does in ours?
Y = Young. How do you show your younger characters to be younger without spelling it out? By the way in which they speak? How are the young treated in your fictional world? Are they encouraged or despised? Is there child labour?
Z = Zest. Do your characters have zest for life? Where do they get that attitude? Have they always had it or do the adventures you set them on spark something within them which means they develop this and, as a result, inevitably have other adventures?!