Take a look at this thread:
https://www.mobileread.com/forums/sho...d.php?t=184118
There are georestrictions which may or may not be gotten around of by using a VPN with Japan IP address and registration to kobo/Rakuten using a Japanese address with the VPN. Hopefully if someone tries it out (already having the VPN) they can confirm whether or not it works...
I would try but cannot read/understand Japanese on the Rakuten Kobo site.