Nature

The characters nature is a one or two word description that sums up their nature - their true self. A person's nature is implicitly tied with the way they see the world and their own role in it.

Demeanor

The characters demeanor is a one or two word description that sums up their demeanor - how they show themselves. A person's demeanor is associated with how other people see them and how they interact with the world.

Nature vs. Demeanor

At first glance nature and demeanor may seem to be the same things, but they are not; demeanor is how the world sees you and how you normally behave, nature is how you see your self and the world only sees it when you are being "true to yourself". Sometimes a person's nature and demeanor are the same, sometimes not. In game terms, a characters demeanor is they way they normally behave, and a characters nature is the way they regain lost willpower.