Okay, here's a pretty quick fix idea.
The work that
Kinboat's
Industrial Legionary is based on provides a pretty good place to start from, conceptually. Change the uniform a little so it reflects something a bit more akin to
WWII or so Japanese uniform. This wouldn't be so important since a lot of detail gets lost at the scale difference.
Now move the Gladius to the other side of the uniform and replace it with an Officer's sword (IJA swords, although shaped like a Katana or Tachi, were built differently [no wavy edge] that can be used for a Banzai charge death animation or some such). Then give him a rifle, light MG, or SMG of some sort, and lastly do the head detail. Emulating the style of the Legionary art, make the most prominent difference the helmet. Modernizing
this slightly would work quite well. I wasn't able to find a good image of one of the faceplates but this includes an alright one. Simply take the demon faceplate concept and merge it with a
suitably evil looking gas mask and you're in business (more angular eyes, concealed filters in the mask, geared a slight bit more to style of functionality).
Finish it off by giving him gloves or some such to prevent skin irritation in a chemical attack and various other assorted pouches, grenades, etc. It wouldn't be all that hard to pull off given a bit of time and skill.