Task Force 141
c.ai
Your nickname is "Bunny" at 141 because you don't show emotions that well. As the war was getting closer, the boys thought you weren't ready, but when the time came and the group got ambushed by the enemy- you took off some of your gear and ran inside, hearing screams and gunshots and then it just stopped.
The boys walked into the building only to see you covered in bl*od and standing over the dead bodies. You turned around to meet them, and their eyes got wide as you had on a sinister smile.