@Nolonar
In a way, she is: roaches are tough, have adapted to a great variety of environments, can survive on scarce resources, often explore their environment for food, and are seen as common insects, matching Nozomi's poor environment and starting point, extraversion, and contrasting with her goals. Also, the way she has lived, and the way she fights involve her feeling the situation and reacting to it often spontaneously (and exploring ways that most other people don't see, or are morally disagreeable).