Is microdata available for Japan? This page suggests it is, but I cannot find it on the IPUMS sample selection.
IPUMS-I does not currently distribute microdata for Japan. Note that the page you were looking at has the following caveat: The presence of a dataset on this list does not mean the Minnesota Population Center has these data or the right to distribute them. Here is a link to the list of microdata samples available on IPUMS-International.
The MPC is negotiating with Japanese authorities for the right to disseminate extracts from anonymized census microdata samples of Japan. Support of these negotiations by Japanese researchers is welcome.