Caius tops the charts of people to worry about. He is impulsive and acts before he thinks and would do absolutely anything to protect the people important to him, and Mia sees that getting him into some trouble in dangerous situations. It took her a while to understand that his grumbled criticisms of her actions - "don't be so stupid" style - were an indication that she mattered to him, but once she did, it turned endearing pretty quickly. Learning about his family situation makes her that much more protective of him in return; she respects his ability to be so exuberant and happy in the face of a painful past like that.
Caius