Until in Shinovi Versus, she had to defeat Yozakura or her parents will be killed, however Yozakura would only accept defeat if Katsuragi killed her. All of this time she has been looking for her parents who were also ninjas as well and they are are alive. Especially since up until this point she's been portrayed as an emotionless loner, (And the anime made her look like a psycho) her surprisingly sad background really comes out of nowhere.
Just about all of the girls' backstories count, but special mention goes to Hikage.