Erisia, in one word, is driven. She is a perfectionist. She wants to be the best at just about everything. Despite this she is not condescending and doesn't brag about her skills, instead she lets her abilities speak for themselves. Erisia's main drive is to become a Mobile Suit pilot, something that she puts more effort into than anything else. She tends to resent those that challenge her position and she feels rage towards herself when she fails to meet her own expectations.
After she joins the Titans, Erisia is turned into an Enhanced Human (Artificial Newtype). Her abilities are dramatically heightened, however, at the cost of extreme mental instability (a side-effect typical in most Enhanced Human subjects), and becomes obsessed with defeating Asuna Elmarit.