Japan dramatically relaxed the green card regulations a few years ago.
Now you could get the green card by investing in Japan with 1 year stay (earliest)
The government is not selling the green card but you can
intelligently leverage the real estate investment for the preferential treatment.
Again Japan is not selling the green card.
However the real estate investment (or any other type of business
by establishing your entity here) should work if you are willing to invest and create your start up in Japan.