Thanks for the comment. My first choice was the Sony but I've tested it here in Italy and it has no Japanese font... I have to buy it there in Japan next time I'll go.
I have difficulties in buying kobo from Italy so I'll go check Booken soon if Borders cannot unlock my order before the out of business...
Japanese books are also written horizontally, mainly ebooks, since it's simpler to manage.
I use everyday LibreOffice and my wife is Japanese so I know all the tedious problems of fonts, encoding, directions, ... That's why I've searched hard and decided for Kobo.
What do you think?