Casimir

At the beginning of their journey, Aria knows little about Casimir. He reveals little about himself and the purpose of their secret mission because he knows that this knowledge could be very dangerous to her.
Given the quality of the armor and sword he wears, and given his cold and haughty behaviour, she assumes he is a highborn.
Even if she knows little about him, she can feel he is an honorable man and a skilled warrior.