It is time for your characters to face their fears and overcome them! Or not.
Does your character cower away when faced with their greatest fear or do they confront it? Do they overcome their fear? How did they get this fear? Have they faced this fear before? Do others accept their fear and try to help them or are they shunned away because of their fear? Do people take advantage if their fear?
So many question that your story can answer. Your story doesn't even need to answer, leave your characters background or even current situation a mystery, if you want. Be creative and create anything you want that revolves around fear.