RetireJapan

That is a great question. I believe it is designed to apply to people making a 'permanent departure' but I have no idea how it would be handled. Actually kicks in next year so might be interesting to ask the tax office about it (please report back if you do!).

Others will correct me if I am wrong but my understanding is that it only applies to Japanese citizens and permanent residents (for visa purposes, not tax purposes) who leave Japan permanently and only if you have more than 100 million in designated assets. Since Japan only taxes residents (not citizens) on worldwide income, I presume there is a process to declare yourself a non-resident so as to ensure you have no further tax liability on future income earned overseas. I wonder if anyone on this forum has left Japan 'permanently' and if so, whether they had to file any documentation to the tax office. In Canada it works this way as there is an option on the Income Tax Declaration to state that you intend to become non-resident.

Is this the same "Exit tax" as the one implemented since 2015 or the 1000 yen "Tourist tax" starting this year.

I assume its the former and I have found an English summary below. On the second page is a summary and who it applies to.
https://www.mof.go.jp/english/tax_polic ... 7_1516.pdf
It applies to those who have been a resident in Japan for 5 years in the last 10 years prior to the 'exit' date and those who have more than 100 million yen in securities, unrealised margin trades, derivatives whether gains or losses. (mentioned in the Japanese version below.)

The Japanese version goes into more detail regarding how it works.
Here it is for reference: https://www.nta.go.jp/taxes/shiraberu/s ... pdf/03.pdf

The Japanese version however mentions exceptions to the above rule for certain resident statuses such as professors and also permanent residents etc.
So it seems you might be right in thinking that it only applies to mostly Japanese citizens but I could be wrong.

When I left Australia, I submitted a document to declare I was a non-resident for tax purposes though I still have a declare my Japanese income and Japanese residency to them as to avoid double taxation.