Hanji Zoe is a Squad Leader from the Scouting Legion. Hanji conducts research on Titans and, as such, is deeply interested in Eren Jaeger, who can turn into a Titan.
Hanji is very passionate and driven in pursuit of new knowledge. She can be seen as very hyperactive, often diving into projects without thought for personal safety (and frightening lots of her subordinates in the process), instead preoccupied with observing and documenting their subjects. Some misunderstands these acts of hers as eccentric and having more than a few screws loose in her head. She also enjoys discussing this research, but as the lectures can be very long and detail-oriented, not many fellow soldiers find them interesting.
Hanji is often excited by Titans and is always eager to experiment with them, coming off as extremely emotional regarding titans. For example, she cried at the amount of pain being caused to a Titan during experimentation. She explained this sympathetic reaction to Eren as a result of the drive to see titans from a different perspective and learn new insights that would normally be overlooked from the traditional view of rage.
However, she still cares deeply for humanity, and takes threats to comrades very seriously, as seen when Pastor Nick is confronted for his coverup of the Wall. When he refused to talk, Hanji grabbed him and held him over the side of Wall Sina, explaining that lives were lost because of him and his religious faction and stating an utter contempt for the priest.