Dust was originally a Mobian Wolf who was part of the Resistance against Eggman; Throughout the war, he lost more and more of himself in a literal sense due to injuries sustained in multiple battles. Rather than wait to heal, he'd simply get robotic replacements so he could continue fighting.

Eventually, after seemingly sacrificing himself by using a Phantom Ruby Prototype to stop a false sun from being dropped on everyone, rendered unconscious and practically in a coma, he was captured by Eggman, who then turned him into a mostly robotic life form, powered by the same Phantom Ruby Prototype he had used to stop him.

Eggman had intended to erase his memories and turn him into a killing machine against his allies, but it was thanks to Infinite he kept them. Though upon realizing what he had been turned into, that he had survived his own sacrifice and yet that sacrifice hadn't hadn't insured Victory, Dust no longer simply wanted to defeat Eggman.

He wanted him dead.

He arrives just in time to help defeat the Death Egg Robot, however he ends up getting ahold of the Phantom Ruby rather than let it be destroyed, at the time not knowing what to do with it, though he didn’t let the others know he had it.

Sonic and the others were eager to celebrate their victory, Eggman once again beaten and defeated, but Dust wasn't satisfied. He attempts to chase Eggman down, but upon confronting him and readying to kill him, he’s stopped by Sonic. Dust lashes out, and the two brawl. Eggman gets away during the battle, and the two end up exhausting each-other. Dust flees, feeling betrayed by Sonic.