I've seen this problem solved a few different ways.

1) Have a romanized version of the value to sort. 2) Have a hiragana or katakana version of the value to sort (hiragana > katakana > roman order for sorting).

Excel seems to sort things without telling it the reading for something. In JS and a few other languages Japanese is sorted based on UTF-8/16 code. This works for everything but kanji because of the reading requires a human.