Reading Japanese in traditional style, vertically from top to down, is possible. Calibre does not support this. With PDF it is possible to read Japanese vertically, but marking Kanji and looking them up in the dictionary does not work. The following procedure produces .mobi files, appropriate for reading and marking.
As input, UTF8 textfiles can be used. Or the .zip files obtained from aozora/青空, a library with free Japanese content, kind of Japanese “project gutenberg”. The following method provides these benefits:
Getting UTF8 txt files displayed on the paperwhite and beeing able to use the japanese→japanese dictionary: