[FairyKing]

At the end of Drive, IIRC the Tridoron and the rest of Krim Steinbelt's technology was sealed away beneath the Drive Pit, to prevent it being used for evil again, right? (And then of course brought back up in every crossover they want Drive in.) So, imagine a story where someone wanted to turn the Shift Cars into weapons of war.

Shift Soldier, a yellowish-tan Shift Car based on a military car. It was designed to be mass-produced to create an army, and as such has an aggressive personality.

The first is given to Shinnosuke, who uses it to become Drive Type Soldier and fight against a new kind of Roidmude. But then, it turns out the new Roidmudes are fakes, created by the same people who created Shift Soldier, with the goal of using Drive to test its capabilities. By the end, the Riders have to fight against a squad of enemy rider troops all using clones of Shift Soldier in some new transformation device to become Mashin Soldiers.