Hey, a real coup there!
I have seen the stuff they printed for the Philippines and for Hawaii, but never for the Western Pacific area as you have.... or should I say, the remainder of the Greater East Asia Co-Prosperity Sphere?
The ones I have seen are not the finest engraving or printing jobs ever done, but the PAPER definitely sets them apart. Americans tried counterfeiting the stuff but couldn't get the paper right, so they just let the occupying authorities inflate it out of existence all by themselves. Took longer, but it worked.
What I would really like to get my hands on would be some of the Britishcounterfeits from War Two that were destined for use in Ethiopia and other places under Occupation: the London-struck Maria Theresa Thalers and the 23-karat Queen Victoria sovereigns! Wouldn't mind half a ton or so of them, come to think of it, even if there were a few duplicates!
But you have obtained a little treasure of your own.
Pics?
I don't think Hirohito's gonna sue you!