7.5.9.5 Defining Japanese index sort order
Japanese is not sorted by the Unicode character order of the displayed glyphs, which are usually katakana. Instead, it is sorted according to the pronunciation of the words, as given in a different script, kanji. Mif2Go has no idea what the kanji is, so you have to provide it by the usual FrameMaker sort order method, in square brackets for every single index entry. Naturally this requires a Japanese native speaker. Once you have all the kanji, and have the Japanese version of the SortOrderIX entry on the FrameMaker index reference page, you should be able to produce a sorted index in Japanese.
You might be able to convert the katakana to kanji with software assistance; see:
If you are adept at Perl programming, you might be able to adapt the following Perl module for this purpose:
http://search.cpan.org/~dankogai/Text-Kakasi-2.04/Kakasi.pm
> 7 Producing on-line Help > 7.5 Configuring index entries for Help systems > 7.5.9 Customizing index sort order > 7.5.9.5 Defining Japanese index sort order