"Step aside," Mara hisses from behind the mask, and you protectively shield the unconscious Damian away from her sword. "This doesn't concern you. So get out of the way."

You were already aware of the history of between the two cousins, and after Mara had managed to sneak up on the both of you, you were determined not to give her any other chances. Damian was a member of the Titans, and so were you - you had to protect your teammate.