Jace

X5-798, or "Jace" was a member of Max's X5 unit in Manticore, under the command of Zack/X5-599. Though she followed her unit to the window, Jace hesitated and eventually refused to escape with the others. She was the only sibling of Max who was left in Manticore, and along with the remaining X5's, she was taught to hate the '09 escapees.

Female Troubles
Jace was the X5 assassin assigned to kill a former member of Manticore's staff. While working on her mission, Jace encounters Max and, after Max stopped her from killing Dr. Adriana Vertes, she fell back to properly assess the new situation. During her next attempt to kill Vertes, Jace fainted, and Max learns from Vertes that Jace is pregnant. Later, Jace reveals that the baby's father was one of the scientists at Manticore. Max tells her that if she returns to Manticore, the baby will be taken away from her, and Jace agrees to go AWOL.

Unfortunately, Vertes betrays them and calls Lydecker, who shows up at the safe house where Jace is and reprimands her for her disobedience. Jace claims that she had no plans on abandoning her mission, but saw the opportunity to retrieve Max and decided to play along. Lydecker agrees that it is a good opportunity and orders her to call Max. When Max arrives, Jace signals her to escape, and they both get away from Lydecker.

Logan Cale set her up with new identification and money, and Jace leaves for Mexico where she can raise her baby. Gratefully, she tells Max before she boards her bus, that no matter what, the baby will be named after its Aunt Max.