The Junkyard Dog MK III is Sol Badguy's main weapon in Guilty Gear Vastedge XT and Guilty Gear Xrd -SIGN-. The sword has a rectangle-shaped blade, and a red and white color scheme. It also has a secondary function as a long-range weapon that can fire a high-level energy spell called Saint Oratorio.
Junkyard Dog MK III is a combination of Fireseal and the Flashing Tooth, which further amplifies Sol's fire magic. After retrieving the Flashing Tooth from Harden Fortress, he had it developed on the recommendation of Dr.Paradigm in order to create a "micro-delivery system" for the ultimate spell, the Saint Oratorio, which is a Magic Art specifically created to work in concert with the OutRage. Sol has also modified Junkyard Dog MK III to reconfigure into a long-range cannon that can fire intense magical burst of energy, this spell being known as Saint Oratorio, which is a powerful Magic Art specifically created to work in concert with the OutRage. 
- As a coincidence, in the older Guilty Gear games, the Fireseal's appearance resembles a gas lighter (much less so in Guilty Gear 2: Overture), while the Junkyard Dog looks like a Zippo lighter. When the casing of Junkyard Dog is unlocked, it resembles a dragon's maw (likely an intentional reference to Sol's Gear form).