>there are several dozen base characters (of one or two different widths) and two or so accent marks. There might be no spaces, you break lines whenever they ru

>there are several dozen base characters (of one or two different widths) and two or so accent marks. There might be no spaces, you break lines whenever they run out without considering word boundaries. You're forgeting about small kana which can be arbitrarily appended to the big kana. Regular words only have one or two small kana after a big kana, but technically there can be arbitrarily many. Either way, they affect word-breaking.