I did some experimenting here.
To my huge surprise, I was able to:
- use my previously created Kobo account to login to
https://www.kobo.com/jp
- purchase a book - which, for some reason was free of charge, must have been some promo programme
- purchase another book, paid with an European debit card
- sync purchased books to both Kobo eink reader (Aura 1) and desktop app.
As far as I can tell, everything displays correctly on the device. I have tried to add those books to Calibre, but they look scrambled on the desktop. For what it's worth, the structure seems to be there (TOC, chapters), it's just the text that's wonky. I'm not sure if it's encoding, font or DRM after all. I have Apprentice Alf's plugins installed, so I'd expect the DRM not to be a factor here.
If someone is interested in playing with those epubs, let me know.