Over the course of the Dragonsong War, Grace had seen Ishgard’s cruelty to its lower classes with incomprehension. Nature inflicted suffering aplenty, but never for its own sake — the wolf killed for food, the bear lashed out to protect her cubs, harm was always a means rather than an end in itself. She had no framework from her isolated forest upbringing in which to understand why these holy knights hurt people for the sake of hurting, so it sat in the back of her mind as a growing sense of wrongness.
Finally, around the end of Ishgard’s war, she found the corpse of a Dark Knight. She had recently started training as a Sage, her first magic job, and the combination of the slain fighter’s soul crystal and her growing magical powers were enough for that part of her that objected to everything that was happening, to the pointless errands and the Echo visions of burning to death and the cruelty of the powerful to the weak, to gain its own identity. And thus Fray was born.
The raid on the Ishgardian holy knights she immediately carried out over their treatment of a defenseless commoner was Grace’s defining moment as a Dark Knight, and ever since then, that part of her has insisted that she should fight as one whenever she encountered cruelty or abuse of power. Her first major battle as a Dark Knight was when she stormed Doma Castle to put an end to Yotsuyu’s reign of terror, but less than a year later when she was pulled into the First, she spent the entire struggle against the sin eaters and Emet-Selch as a Dark Knight. Using powers of darkness against elemental light seemed fitting, but also the presentation of the sin eaters as being holy entities bestowing forgiveness on sinners was another form of cruelty and abuse of power. And Emet-Selch’s cruel and mocking manner only heightened her outrage.
The struggles she’s been through since then have not called up her dark side in the same way, and these days she only fights as a Dark Knight often enough to keep in practice. But Fray is always there, ready to step up when the time to fight abuse comes again.