Characters actually - it's a standard Garlean weapon type. However it's usually only reserved for crack troops like Imperial Centurions, and Legati like Gaius. Regular grunts usually use more mundane weapons like swords and spears. And for that matter, the Garlean gunblade is basically just a pistol with a long sword blade attached to the side of the barrel - it's nothing like the FFVIII and XIII version.

And speaking of FFXIII, Lightning's gunblade the Blazefire Sabre is actually useable by players - it's the GLA/PLD FFXIII weapon gained through the 'Lightning Strikes' event which will be returning tomorrow. Unfortunately though, it's still just a sword weapon - the gun part is non functional, making the weapon nothing more than a sword with a fancy fold out blade. But it's still cool nonetheless.