Any bones on Japanese soil should be reported to the Japanese police. If on a US base they need to be reported to the MP's. Just like families would like closure in America, the Japanese are no exception.
Digging up ordinance on land there is DANGEROUS. There are mortars, bombs, phosphorous grenades, regular hand grenades and LOTS of other dangerous items. You expose a phosphorus round to air after all these years, it won't be pretty.
I was there from 1978 - 1980. I played with stuff underwater but not on land. You are messing with fire digging up land ordinance.
In MY opinion, you should stick to the water finds.
I found pineapple grenades underwater. I broke off the tops and emptied them underwater. I rolled over a depth charge, played with a huge naval round and tried to make a torpedo explode by bringing it to the surface and setting it free in super deep water and swimming like crazy away but it didn't explode. Yes I was younger and more foolish but I had a blast over there. Luckily I never got blasted by the stuff I played with.
If you are in the military over there, nothing you find can be brought back to the states. Anything that is or was an explosive device is illegal to bring or send back. That was the military law then and it probably hasn't changed.
. And I'm asking for a friend...what do you do when you find remains of a human skeleton? Is he legally bound to report it immediately if he should find one? 
