Vector, operating under the aliases Gabriel Miller and Subtilizer, emerges as the primary antagonist in the Underworld War. An American VRMMO player, he is recruited specifically to invade the virtual Underworld. Diving in as Subtilizer, he wages war against the Human Empire Defense Army, fighting alongside the Dark Territory forces as their key adversary.

Demonstrating formidable combat prowess, Vector clashes with the Integrity Knight Bercouli. In their confrontation, Bercouli employs his Time-Splitting Sword against Vector's past, seemingly destroying his present form. Undeterred, Vector later returns to the Underworld as Subtilizer to renew hostilities.

His involvement extends to recruiting thousands of players from the United States, China, and South Korea, funneling them into the Underworld to assault the Human Army. This mass recruitment critically tips the numerical balance against the defenders. Vector's persistence and ability to re-enter the virtual conflict solidify his role as a recurring threat.