How do I take a cold calculating character and make them more human over time?

My characters have known no empathy or love their entire lives, being treated more like living weapons. All they do really is take orders and have horrible things done to them but to them it’s normal. I want my MC, after finding her file and real name, to go rouge and slowly realize how messed up her life was. I want her to become more human. How do I achieve this?