Since I have been asked to do sensitivity/cultural reads a couple of times now, it seems sensible to set out what I think that involves, what I can (and can’t) do, and what I think it should cost.
What It Involves
I will not do your research for you. I expect to read a manuscript containing all the cultural details you want to include. You should be hoping that I will send it back with the comment “This is all fine. Well done”.
One exception is that I will, on request, come up with a small number of appropriate Japanese names for you. This is basically impossible for people who are not fluent in the language, but not that much effort for me.
I will comment on things that are mistakes, and things that look implausible but might be true in a particular case. In some cases, that means that I will ask for your source for something, and I may tell you that I think your source is unreliable.
I will comment on particular points that are likely to be offensive to a significant number of Japanese people. There are oversensitive Japanese people, and Japanese people who are not bothered by anything, so I will do my best to take a middle path.
I will also comment if there is an overall approach that is problematic. This may not involve any specific problems. An example would be the treatment of Japan in Shadowrun. It is, like every country in the game, dystopian, but that dystopia is based on American wartime (and post-war) propaganda about Japan and the Japanese, not on what Japan is actually like. If this sort of thing is a problem, it is likely that it can only be fixed by completely rewriting the manuscript, which may not be an option.
Which leads to my final point. It is up to you to decide what to do with my comments. You may decide that you want to be offensively inaccurate on a particular topic. As a specific example, the US consensus view of Yasukuni Jinja is offensively inaccurate, but you may decide that you do not want to offend your American audience, and that possible offence to Japanese people who are extremely unlikely to ever read your product is a price worth paying. Thus, I hope that you will consider my comments (it’s a waste of money if you don’t), but I do not claim the authority to require changes, nor will I make a public fuss if you choose not to change something. (Although I do reserve the right to say that I pointed something out but you didn’t change it if someone criticises my feedback on the basis of the final product.)
What I Can (and Can’t) Do
I am Japanese, and resident in Japan, so I can comment on things set in contemporary Japan.
I am fluent in Japanese (I have been paid to write in Japanese, and to give a lecture course on logic at a university in Japanese). This means that I can comment on use of Japanese terms.
I have a good general knowledge of Japanese culture and history, so I can also comment on cultural and historical aspects. I have a substantially better knowledge of the Heian period than of most others.
I am an expert on Shinto, particularly contemporary Shinto, so I can give you more comments on this topic than you could possibly want.
I am not an expert on Japanese martial arts or military history. It’s fine if they come up as part of the background, but if they are the main focus, I am probably not the best person to ask.
I am ethnic minority Japanese, and spent seven years or so serving on local government committees dealing with the issues faced by non-Japanese residents (both as a non-Japanese resident, and as a naturalised Japanese), so I can comment on portrayals of ethnic minorities in Japan. Note that the Japanese situation is completely different from the US situation; ethnic minorities here face different problems. Thanks to my service on the committees, I do know quite a bit about the problems faced by ethnic minority residents of ethnicities other than my own. (I am also an immigrant, and thus can comment on the immigrant experience here — the other experience in this paragraph also applies.)
I am not Japanese-American, and I cannot comment on what they may or may not find offensive. It appears, for example, that a substantial minority of Japanese-Americans are offended by people not of Japanese descent playing dress-up in kimono, while the Japanese overwhelmingly think it is wonderful. Note that, if you are writing in English, it may be more important to avoid offending Japanese-Americans than to avoid offending the Japanese.
Japan is very diverse, just not in the ways that Americans normally mean when they talk about diversity. (Non-Asians make up less than 0.5% of the population; non-Asian Japanese less than 0.1%, and probably less than 0.01%. For fictional purposes, I don’t exist.) Greater Tokyo is different from Osaka is different from rural Aomori. Okinawa is particularly distinctive, and I am probably not the ideal choice for something set there. Similarly, while Hokkaido as a whole is sufficiently similar to the rest of Japan for me to cover it, I would not be ideal for something specifically concerning the Ainu. I may, nonetheless, be the best you can get.
I can comment on fantasy analogues of Japan, or science fiction or alternate history versions, based on the background outlined above.
On a completely different topic, decades of writing for and editing Ars Magica mean that I can still comment on things set in medieval Europe or a close analogue.
On the other hand, it is now around 20 years since I lived in the UK; I am no longer capable of doing a sensitivity read for the contemporary UK. (If you are more interested in the twelfth century, or even the late twentieth, I’m your man.)
What I Charge
A sensitivity read should be easy for the person doing it. If it isn’t easy, then you aren’t really qualified to do this sensitivity read. (If that happens, I will say so. If a manuscript goes deeply into a field of Japanese culture or medieval history I do not know well, it could happen.)
Thus, I think I should be paid about 10% of what the author is paid to write the manuscript. It is entirely possible, particularly in TTRPGs, that this will not be enough for me to do it. However, I want to support accurate and sensitive portrayals of the cultures I know, so it is worth asking, and I may take it on even if I do not think it is likely to be financially worth it.