The helmet is a civilian model helmet, the badge I think is police. The kempeitai, being military police used the military model helmet.
Posting on the Japanese part of the forum might get you more responses.
The canteen looks like a nice condition SNLF canteen.
I have moved your thread to the Japanese part of the forum.
You are likely to get more response here.
Searching for anything relating to, Anton Boos, 934 Stamm. Kp. Pz. Erz. Abt. 7, 3 Kompanie, Panzer-Regiment 2, 16th Panzer-Division (My father)
Thanks! The 'story from the vet' (same owner, 74ish years) is that they were picked up from the same location in the S. Pacific - not off the same soldier but from the same island campaign. No papers of course but I don't think the helmet shield was replaced. Would a civilian police helmet be unheard of outside of mainland Japan as part of an MP or other unit?
Not police nor MP, but normal civil defense, who dealt with protection of the population from air raids. Note that the insignia features cherry blossom petals between the sunburst, setting it apart from police and kempei. They could have been active in any area with a civilian population, so a Pacific island is not impossible. But even patriotic women's group sashes are being claimed by vets as having come off dead soldiers, which is total nonsense, so such stories should always be taken with a grain of salt. The inside writing says "3rd division (of civil defense)", which makes it sound too elaborately organized for a small island, so I am fairly sure it comes from a city in the mainland.