Born and raised as Eglantine Vandham, she grew up surrounded by Bretonia's high society, taught by some of the best teachers in the House. She spent most of her time on her studies, finding joy in art, and as she grew older, mathematics and science. From what little time she spent with popular Sirian media, she took to the long-running Kusari Kamen Rider series, something that would forever inform her taste in technological casings - particularly for gadgetry.
Eglantine continued her studies into her teenage years, and it was around this time that she'd properly gotten into working with electronics. Programming robotics systems, building mechanical arms, making little model spaceships that she flew around the family penthouse. She became quite passionate on the subject, going so far as to shun her time in the high life to spend hours in the workshop or holed up at her desk writing lines of code.
This angered her parents, who wanted a dainty little socialite, rather than a woman with knowledge in things only the "common man" would bother with. She refused to conform, however, and the rift they created would only grow as time went on. Eglantine continued her studies, and steered the direction of her research towards mechanical transhumanism, knowing full well if she escaped Bretonia in an organic body that it would be all too easy to track her down. Fingerprints, retinal scans, hair samples, blood droplets, dandruff... Too many liabilities, especially when combined with her Neural Net pings.
When she wasn't neck-deep in her studies, she was busy engaging in all sorts of combat training, taking up the katana after discovering a particularly old series of Kamen Rider in which one of its antagonists wielded the weapon when undercover. She took up the bow later, if only because her parents insisted she needed something more traditionally Bretonian.
Eglantine would spend a number of years formulating and improving her design, and befriending people willing to work with her for the right price. She'd had the foresight to create a portable assembly rig to go with a suit of battle armor she'd made on a whim to fit the shell of her new robotic body, and got her hands on a pair of well-crafted mechanical weapons.
Just before she would come of age, and be forced to remain in Bretonia to deal with the pressure of carrying the family name, Eglantine decided it was high time she would be no longer. Shedding her physical humanity in a very stressful six hour procedure that somehow, somehow went off without a hitch, it was with the ditching of her old body that she left behind that name. No longer would she be the heir to Vandham, nor that daughter of old money. She was now Briar, having christened herself such from the meaning of her birth name - Eglantine being another name for sweetbrier.
Promptly fleeing Planet New London, she went to join the Junkers just a hop-skip-and-a-jump away at Trafalgr Base, always eager to receive another knowledgeable mechanic into their ranks at any rate. Briar took to the workflow quickly, welcoming the chance to dunk on Bretonian society considering she'd practically ditched it by that point. She went out of her way to conceal her lack of humanity, projecting herself as a private person despite her spunk, and passing off the remarkably robotic limbs as simple augments, built to work much better than any human hands could.
Briar was, however, nothing if not rarely satisfied. She eventually grew tired of the system the Junkers had built, toeing the line of House laws, and pirating in space well outside the jurisdiction of those Houses they had allied with. So, she took her ship and left. She migrated to the Foyle Shipyard, where she stayed for a time to install her personal armory into her Combat Service Freighter. After that? Briar left once more, setting out to wander Sirius until she'd found herself somewhere more comfortable than the stifling cage of Bretonian aristocracy while she stuck to the habits she'd picked up under the Junkers.