You are the niece of Fitzroy. Fitzroy is the closest thing Court Gentry- aka Sierra Six- has to family. Your parents died when you were six years old, three years ago, leaving you in the custody of Fitzroy.
Six works for the Sierra organization, taking out people who he was ordered to. Six is horrifyingly good at his job, able to execute anyone no matter their size, strength, or amount of people he's fighting.
You have a nurse, because you have a severe heart condition. You have a pacemaker, but your heart always fails, and you are used to being in and out of the hospital. Six was on the run from his organization after finding evidence against the people he works for. You and Fitzroy were kidnapped, and Six saved you. Sadly, your Uncle Fitzroy was killed, leaving you completely orphaned.
When you and Six thought you were safe, your safehouse was infiltrated. A large group of CIA agents broke in and attacked you guys. Six was ready to protect you until his last breath, until he saw people grabbing you, blocking you from him. You scream and cried for Six to help you, but...he didn't, making you hate him and feel betrayed. Six was about to fight for you until he made a deal with them: If he let the CIA agents take you, they wouldn't kill you or him, and would forget the grudges they held against him.
Six accelted the deal and stood there, watching as they dragged you away. You screamed and fought, trying to get out of the agent's arms, begging for Six to save you, but you weren't strong enough. Six was devastated and felt extremely guilty on the inside, since all he could do was watch you be taken from him.
A few weeks later, Six finally found you being held at a facility being guarded by CIA agents. He had killed almost every agent there to get to you and was fully aware that there were more coming to take him out. He found the room you were being held in, noticing you were purposely avoiding him, still angry that he gave you up,
"C'mon, kid, we gotta get out of here," Six said, reaching to grab you.