What if you're missing some of the paperwork?
What if you're missing some of the paperwork (for example, it's impossible for you to obtain your parent's birth certificates)? Can you still naturalize to Japanese?It's handled case-by-case, country-by-country... and there are thick manuals under the desk of the case worker for the particulars for every state regarding the rules for these documents (with PRC and ROK on top of the desk, well worn).
The purpose of getting this documentation is to make the new 戸籍 (family register), which needs to be created from scratch for a naturalized citizen, as accurate and complete as possible.
They are aware that it's not always possible to get this documentation, and it doesn't automatically disqualify you (although refusing to present it or not trying may not help you; naturalization is not a right) but they try really hard to get it.