At the beginning of her memoir, Catalina is a young woman living in a convent, on the verge of taking her vows to become a nun. She eventually transforms herself into a soldier with a male persona, adept at killing both on and off the battlefield. In positioning herself as a man, she exhibits many stereotypically male traits, including bravado, competitiveness, and aggressiveness. She possesses a quick temper and responds to insults with her sword. She writes very little about her feelings—her memoir is almost entirely devoid of introspection. She appears to have no compunction about killing men for reasons as trivial as offending her over a game of cards. Despite the fact that she generally depends on violence to solve problems in her day-to-day life, she is very intelligent, and many times she survives by using only her wits. She moves from place to place regularly, never settling down or developing close relationships with others, perhaps for fear that they will discover her greatest secret—that she is a woman.

Although Lieutenant Nun covers more than twenty-six years, Catalina shows very little personal or emotional growth. The Catalina at the end of the memoir is nearly identical to the Catalina from the beginning; the passage of time is apparent only when Catalina writes that it has. Her development is primarily in terms of the violence she commits. She becomes a better soldier over the years, and she also becomes more readily able to kill at the smallest provocation. Despite her abilities as a soldier, or perhaps because of them, she rarely expresses emotion. One of the few times she describes how she feels is when she expresses joy about meeting her brother. Another is when she is plunged into despair after killing him. Catalina’s life, and her secret identity as a woman, doesn’t allow for many intimate relationships. Her relationship with her brother is the most important relationship in her life, but she devotes only a few words to it. Catalina clearly values her skill and prowess as a soldier and as a man far more than she does her emotional development, which she likely associates with her biologically designated gender—one she has worked so hard to hide.