The problem with CD games, is that there tends to be a lot of garbage in between the used areas in the data track. It can be old code, other game code, even 16bit wave data. This is very common.
Anyway, the point is - set a break point for the Get_Font bios call, and step back to the code that called it. Trace that back to where it reads the SJIS string. Also, dump CDRAM and look for sjis in that. It makes it easier to identify/match up in the ISO, so you know what points in the ISO to edit.