Russell wrote:But doesn't this new law in Japan imply that Japan taxes at the source as well?
Liability in Japan is with the beneficiaries. It is not with the estate, so it is not at source as such. That has not changed.
As SJ pointed out, I think it is unlikely that Japan is actually going to be chasing down people in other countries with a tax liability, any more than any other country actively pursues tax liability of people outside the country. The fact that the US has just started doing this has been very noteworthy. However, if that non-citizen non-resident chooses to come to Japan, there might be issues.