Getting hold of its documentation/title..?
It will be a matter of getting
new documentation for it, and that will be affected by the circumstances under which it lost its original identity. Read between those lines.
I've tried to hint at the possibilities for the true situation here but half of my posts have been deleted, throwing out the baby with the bath water. There's plenty 'not right' about the car which is visible from the few photos provided by the vendor. The wider point is that there will be plenty of people in Japan who
do know what this car actually is and who will be able to rectify the situation, and that it is very likely the vendor knows the true situation and is not letting on (and can't, because it would blow the gaff).
If anyone from outside Japan thinks they can get involved in it all and come out ahead then they are kidding both themselves and anyone else who believes them. Like I said before, "Here Be Dragons".