Justice is a major character in the Guilty Gear series. Created by That Man, Justice is the first "complete" Gear with free will and with the power to control all of her own kind. She was the instigator of the Crusades, a hundred-year war against humanity, until she was finally sealed by the Sacred Order of Holy Knights.
In 2065, the U.S. began the mass production and monopoly of combat-ready Gears, and deployed them to allies across the globe, bringing countless lands under its control. In 2073, That Man, the chief researcher of the Gear Project, used the collective information system he had built, hoping to give orders to the weaponized Gears and stop the wars, and designed Justice: A copy created using Aria Hale's cryogenic DNA as a genetic template, according to -SIGN-'s Library. Aria herself, afflicted with an incurable disease, presumably agreed to the Gear conversion.
During her activation test in 2074, her mind and body were forcibly invaded by the malicious entity from the Dawn of Revival. Harvesting her DNA, it infected all of Japan and used Information Flares to force the Japanese people to become Anti-Matter Gears. The spatial anomaly caused reality itself to slowly assimilate into the Backyard. That Man regrettably overrode Justice's control systems and forced her to fire a Gamma Ray at Japan.
Because of this event, Aria's psyche shattered. Forgetting who she was, Justice rebelled. As she ran amok, That Man was able to save half of Aria's soul, but was unable to stop her. Justice took control of her fellow Gears, gathering an army, and declared war on all mankind. In the wake of heavy initial casualties, humans formed the Sacred Order of Holy Knights to combat Justice's forces in a hundred-year war known as the Crusades.
During the war, Justice met Kliff Undersn, Commander of the Order, and they fought on seventeen occasions. In 2173, Justice was challenged by Sol Badguy on his own; Justice defeated him, sparing his life, which led to Sol stealing the Order's Fireseal.
Two years later, in 2175, Justice was met in battle for the eighteenth time by Kliff, who had retired as commander. To his aid came his successor Ky Kiske, who forced her to retreat. As she did, she found Sol and they fought for the second time. Justice learned that he was a Gear and tried to take over his mind, but he was unaffected. In her bewilderment, Sol unleashed his "lava and flames" and made Justice lose power. Ky, who was on her trail, noticed this and had his men seal Justice away in a dimensional prison. Without their master, most Gears entered a dormant state, and many were rounded up and destroyed, finally ending the Crusades.
Five years later, Justice is freed from her prison by Testament thanks to the blood shed in the Second Sacred Order Selection Tournament. In Normal Mode, all contestants fight Justice on the last stage, but canonically she is defeated by Sol Badguy.
When Sol fatally wounds Justice, she seems to regain her memories and her dying words are she wishes that "The three of them could talk one last time". It is unclear whether or not Sol actually realizes that Justice is Aria, but he vows revenge on That Man for everything he has done. The tournament itself is much later revealed to have been a farce orchestrated by the Conclave in order to take control of Justice.
Justice's Story Mode in Guilty Gear XX recounts how she was sealed away by the Sacred Order, thus bringing an end to the Crusades, as a story narrated by That Man.
Her Story Mode in Guilty Gear XX Λ Core Plus is a retelling of her resurrection by Testament in the original Guilty Gear, her last confrontation with Ky and Kliff, and finally meeting her end at Sol's hands. In Story Mode for all other characters, a P.W.A.B. scientist named Crow is shown to have created mechanical copies of Justice, based off of combat data he acquired from the Second Holy Order Tournament, thus replacing the Robo-Ky imitation series.
In 2187, the Conclave - aided by Ramlethal Valentine - retrieves Justice's Cradle from Babylon in order to revive her and reform humanity. After the Cradle's Felion defense and outer exterior are destroyed, it reveals a titanic, armorless form of Justice and vanishes again. Justice is next transported to Illyria Castle, where she will receive the enormous energy from St. Elmo's Fire and be resurrected via Chronus binding his soul to her body.
The Illyrian forces do not stop Justice's physical activation but, with Dizzy amplifying the energy to overload the Conclave's systems, Sol removes Chronus who was rejected by Justice. In the immediate aftermath, her body is retrieved by the Universal Will.
Ariels wants to fuse Elphelt Valentine, a genetic copy of Aria, with Justice in order to create a "perfect humanity". However, her plans are thwarted with the combined efforts of That Man's and Sol's groups. Jack-O', designed to be a physical patch for Justice, receives the Saint Oratorio energy and partially fuses with Justice. However, the unconscious Justice denies becoming human, tormented by her rampage, and Jack-O' needs more energy to override her consciousness and force the merge. Sol decides to power up a second Oratorio with his Junkyard Dog MK III. Although Daryl's fleet almost kills them, Axl Low's time compression and a dying Ariels' protection allow Jack-O' to become one with Justice, turning into a new incarnation of Aria.
And she is voiced by Jennifer Hale in the English dub and reprised by Wakana Sakuraba in the Japanese dub.