Updates for this thread.. sorry, i updated another thread, and i forgot to update this one.
I have returned from my holiday in Osaka, and true enough, the Glo first detects your IP location, before deciding which account to allow you to log in with. So when I was in japan, it only allowed me to log in with my Rakuten id. However, once back home, I reset the unit and started again, and this time it "correctly" allowed me to sign in with my kobo id!
So for the japanese kobo glo, i conclude that it is no different software-wise, from the international version. Same goes for the paperwhite as well!
Thanks for all your suggestions guys!