So I dig in on the subject today and unfortunately I can confirm that most of the Shoken companies in Japan will ask anybody going abroad to have some limitations or to close the account at some point. This is especially true for the online ones. At least, this problem is not only for foreigners but also for Japanese.
You can find detail information on this page for example (in Japanese):
https://yatsuyaku.com/securities_accoun ... residents/
I also found that someone living in Malaysia is using many accounts to invest in USD and transfer in Yen to Japan. He is using Interactive Brokers and FirstTrade (not familiar with this one).
I also found that guy from a small company Global Support that explains one way to transfer money from a Japanese Shoken account to a Singapore establish Brokerer called Philip Capital.
https://www.phillip.com.sg/ They have offices in Australia so this could be one solution to explore for some of you guys. It looks like then there is no issue to access from wherever in the world.
https://www.youtube.com/watch?v=DUGmufR4xkU
That is really another huge subject to explore which could mean changes in investment strategy for many who might have to go back home at some point. If anybody has a solution for someone who may need to go to Europe please let me know (Ireland? Luxembourg?) I have not find anything yet.