Many churches and temples in Ogaki have a sign in the window saying "We will under NO CIRCUMSTANCES assist with third-party ancestry investigations (身元調査)." This is largely because parish records (and the analogous paperwork at temples) can leak burakumin status or Korean ancestry, both things which Japanese people have ample reason to not want publicized about them.

A sidenote:

I debated during college (in the US, prior to ever living in Japan, where I've been for about 10 years now).

I was mildly notorious in debate circles for running a particular "case" (proposed instantiation of a government policy supporting the resolution which one would, as the government side of a debate, have to win was beneficial) on any resolution which would support it. For example, the resolution might be "The government shall limit the information it records about it's citizens." One team of the debate has to convince the judge that they have a concrete idea for how to do that. The other team opposes either that concrete idea and/or says "That case doesn't actually support the proposition our opponents are forced to support."

The case was "abolish the koseki", a family register in Japan which was once considered semi-public information (this has been tightened up rather severely, but it still exists and companies often still ask to see yours) and which has a variety of ways to leak extraordinarily sensitive facts about one's family, in addition to being an odious institution for a host of other reasons. I say "notorious" for this case because, by American collegiate standards, the koseki is straight-out evil, and the reason we chose to run this case is because there are few ways to debate in favor of retaining it and all of them require you to be better versed at Japanese politics/policy than my debate partner and I were, which is unlikely to be true of any US debate team picked at random.

I like to believe that my one lasting contribution to debate is convincing a lot of tournament directors to change the traditional wording in resolutions "The government shall $DO_SOMETHING" to "The United States federal government shall $DO_SOMETHING", because when we interpreted the government to mean "Japanese government" the other team invariably said something along the lines of "That's not what the resolution writer intended", to which I would say "You being ignorant of a major first world nation whose internal political issues are well-reflected in the academic literature may make this debate inconvenient for you to win but that does not mean I'm not allowed to pick something which fits within the clear definition of the word 'government.'"

This drove people nuts.

Ten years later I just had to get a copy of my family's koseki to apply for an apartment lease, upon which the renting agent said "Oh, you're American. Do you even know what this is?" Yep -- funny how life works out. (Why does my apartment renting agent need my koseki? To determine whether I'm the right sort of people to live in the really nice apartment we're moving to. Does "right sort of people" sound ominous to you? YEP, exactly as bad as you think it is.)