However, if you've lived there a while and have a decent grasp of the language, it should be easier to at least navigate the supermarket (I can just imagine myself spending 2 hours trying to decipher kanji...)
Remeber: not all tamari is wheat-free, but there are more wheat-free varieties out there than there used to be (at least I've seen some in import shops here.) I believe Kikkoman has one now, but I could be mixing up brands.
Be careful of sauces in general. I'd say buy ingredients as raw as possible and make your own. Also, no seasoned nori (usually has soy sauce= wheat)
Oh, and aparently someone there is making gluten-free ramen/soba/etc noodles. They have some at the Japanese food store here in Toronto. I can't remember the name, and I haven't tried it yet, but you might be able to ask around.
You can do tempura with corn starch and/or rice flour.
Anyway, as Shadow said, don't go off the gluten until your testing is done (which means time to go out and enjoy whatever you can.)