I don't know about that, I am not an expert on Japanese law, but I'm pretty sure the Japanese government recently announced that they would raise the federal minimum age of consent soon anyways. (I'll send you the article if I find it.)

Edit: couldn't find the article so that might be wrong, but I honestly don't think the truly powerful and rich need legal loopholes if they want to sexually abuse children and get away with it, they usually can just do it and get punished only when their crimes are obvious and outrageous to the public.