I have not heard that before: that Japan may join the ranks of big BTC holders. IIUC, the largest HODLER of BTC is still the USA (although China is producing over 60% of new BTC in recent years).
groll, do you have any references or links that we could read? If Japan gets into BTC in a serious way, that would be huge news.
Check out this site, its a very interesting topic about Japan and Bitcoins.
https://news.bitcoin.com/japan-dominate-bitcoin-landscape/
After reading that article it is very clear that Japan is ready to take on the challenge to be on the top of bitcoin industries leading countries. As of now possibly they will be next to China in Asia. But who knows in the near future they may have the lead in the industry.