Final battle with Justice,
Guilty Gear.
( English Released October, 31st. 1998 )
His exact history is unclear, but it is known for certain that Sol's real name is Frederick, who not only was one of the lead scientists of the Gear project, but is also the prototype Gear from over a hundred years before the events of the Guilty Gear games. As a prototype, he is immune to the orders of Commander Gears. He was personally acquainted with That Man prior to the Crusades. His headband is actually a Gear-suppression device which prevents him from giving into his Gear nature and losing his rationality, at the cost of suppressing much of his power. The headband also conceals the glowing red brand on his forehead, the telltale mark that would expose him as a Gear. In Guilty Gear 2: Overture this headband suppression device seems to have malfunctioned due to I-No's doing (throwing Sol into the past to fight his past-self: Order Sol ) in Guilty Gear XX Accent Core Plus, Sol's ending. Sol seems to have broken or cracked the seal on his headband. This might explain the increase in Sol's strength in Guilty Gear 2.
As Frederick, Sol created the "Outrage", which he called a supreme Anti-Gear weapon. The Outrage is actually not one weapon but several - eight components called "Jinki", which greatly amplify their wielders' magical ability. Only three Outrage weapons are currently known to be active - Sol's own Fuuenken, Ky's Fuuraiken (Thunderseal), and Anji Mito's twin fans, Zessen (Stopping Fans). The other five are supposedly in the custody of the United Nations, although some fans believe Paracelsus, A.B.A's living key, to be a jinki.
Frederick also saved Kliff Undersn (one of the leaders of the Holy Order and the one who named Ky leader of the Holy knights) when Kliff was still a young boy. Roughly half a century later, he was himself recruited into the order, as a bounty hunter named "Sol Badguy." Sol took part in the Crusades, ironically becoming one of the best fighters on the human side. At this time he was a member of the Sacred Order of Holy Knights (Seikishidan). He acquired the nickname "Corrupted [or Immoral] Flame" during that time, a name that such figures as I-No and Justice use for him later. However, he later became disenchanted with the methods of the Sacred Order. At an unspecified time, Sol fled the order, taking with him the Fuuenken, which the Holy Knights had come to consider a sacred treasure. The theft earned him Ky's enmity.
In 2175, Sol faced Justice directly. The two fought, and Justice won - in the process, discovering that Sol was a Gear (but not his true identity as a creator of the Gears). Justice attempted to assert her power as a Commander Gear to control Sol, but was unable to do so. Exploiting her confusion and weakness from the fight, the Holy Order, led by Ky Kiske, sealed Justice away, bringing the war to an end.