[@Sola]
Yeah, I know. My preliminary outline right now is that he was the younger brother of a soldier who was killed in Manila, and has a grudge against whoever did it?

Given the Japanese government installation, it could make sense for him to be a spy-type with knowledge of Tagalog, English, and Japanese but I'm pretty sure your character is already in that niche.

I also need to take the weapon loadout into consideration. Given the Japanese/American conflict in the Pacific would Arisaka/M1903 or Type 100/M3 Grease knowledge make sense?