Fang is a resident of Gran Pulse; Oerba was her village that she lived in. She and Oerba Dia Vanille were chosen by the Pulsian fal’Cie Animus as l’Cie. They were to become Ragnarok so they could destroy Cocoon. Vanille was too afraid to use her power and so Fang attempted to do it alone, along breaking the shell of Cocoon in the process. The Goddess Etro petrified the two of them to make sure they would cause no more damage.
500 years later, they are released from their frozen state. With Fang’s memories of being a l’Cie wiped and Vanille’s still glowing, she sets out to try and help her finish her Focus so she doesn’t become a Cie’th.