It's good that you posted now. I had meant to get with you. I ran into some difficulty with that Christianity during WWII subject. At the moment I got some info from a translation of some paper that had very little on it. It's over in the dozo, and I'll get back with you on the title and page numbers and such, but it really doesn't have much information.
From government pressure the several Chrisitian denominations combined into one group--United Chruch of Christ--and they were pretty much left alone, but watched carefully. On the non-governmental level, it seems there was the occasional local prosecution brought up by those who tried to enforce the emperior worship at local shrines--and somewhat like in the first century, Japanese Christians often refused to do so.
That's all I can get at the moment. I am still looking when I get the time, and I may be able to find something else, and if and when I do, I'll let you know. Sorry to the little and late, but am still in process. As for this question, I will also keep my attention to that point open, but will not make any promises. Thanks gwendy85 san, for your patience.