Almost all military records were destroyed in the fire bombing of Tokyo in WWII. Of those that remain, the authorities here will not release information unless you can prove you are the next of kin of the person concerned. If it is an officer who made it to General or Admiral there are published books in Japanese that show what they did after reaching that rank. In addition, the roll of all naval officers has been published but the amount of information is mixed, and after the Taisho era there is little information held. The easiest is if you have other documents with the certificates which will give you a unit, you can then research the unit rather than the individual. Having said all that, they are still a lovely item and from time to time you can uncover some very interesting groups. Regards, Paul