Ah, well, I can't resist. Here you go with a female Keystonian:
Prisoner 33-T-Sigma (Sigma for short)
During the Toma Operation, the Zealian agents came across a strange girl wandering around Giant's Claw. She appeared plain, with dirty brown hair in a pony-tail, and in her late teens. One of the agents freaked out, believing she was an agent of some force operating against Zeal's wishes (Note that no such force actually existed at that point. This agent was just overly paranoid). He subsequently attacked her, being sure to knock her out rather than kill her. At the end of the mission, she was captured and brought back to Zeal for interrogation.
Unfortunately for both parties, her brutal capture had caused her to suffer amnesia, so she couldn't remember whether or not she actually was working against Zeal. As the interrogator worked on her, he interpreted her resistance as proof she had been trained by a highly capable organization. Consequently, he increased the intensity of her torture/interrogation. Magic users were brought in to use their specialized talents to get her to speak.
It was at this point that things started to go wrong. At first, it was minor an intermittent. A Fireball failed to find its target and circled around Sigma endlessly; an Ice spell fizzled out with no effect. Then, spells started backfiring. Casters would find themselves at the mercy of their own magic. It eventually reached the point where no spellcasters were willing to even be in the same room as her. Eventually, the interrogator gave up and arranged for her to be put in stasis. The stasis chamber was set up, and the she was placed into it. The spell seemed to work, at least at first. Later, when no one was around, it failed for seemingly no reason, and Sigma was freed. It is here that her story starts.
Note: Unlike most characters with amnesia, Sigma holds an uninteresting past. She was just at Giant's Claw out of archaeological curiosity.
Edit: Just a couple of things I thought I should add.
Note: Her ability to resist magic has nothing to do with her being special or anything. It's just a self-defense mechanism that arose from her ordeal.
Combat: Aside from her unique ability, Sigma is quite unspectacular in combat. With her experience spelunking (which she doesn't even remember), she developed a small proficiency with the pick (a short instrument usable for powerful piercing strikes), along with the muscles in her left arm to support it. Her ability, on the other hand, will turn out to be quite useful. At first, many spells and magical abilities will miss her or fail randomly. As she gains experience, she will be able to turn magic back on its caster, or allow certain spells (healing ones) through her guard.
