Heh, this I can actually help you with.
The issue with viewing Japanese characters in ROMs like this is that unless they use standard Unicode, or S-JIS, they are using a custom text encoding
The English you're viewing in other ROMs is probably stored in ASCII encoding and is viewable by default in the hex editor. In order to view other text encodings, you'll need to use a table file
to tell the editor which characters to show for which values.
Typically these values are (edit: one byte :p) in the range between 00-FF, though they can be more if there's a lot of kanji.
Others may be able to help you more with pointer tables, but what I normally use is an emulator with a feature that let's you see video memory, or simple relative searching.
If you take a look in video memory when text is on the screen, you'll be able to see the font loaded into memory. This should be the order that the characters appear in the encoding, and in an emulator like FCEUX you can float your cursor over the character to display its value.
You can also do a relative search to look for values that match the pattern of the values relative to each other. You'll normally want to base this on the order of the font as it appears in memory, or in the ROM as viewed with a tile editor. Lately I've been using Translhextion's "value scan relative" for my searches.
Once you find some matches, typically based on some text you find early in the game, try making edits to it and checking it in an emulator until you've found the text you're looking for. Based on the values, and the order of the font tiles, you can normally fill out the rest of your table file. In a pinch, you can enter values into the text you found and check them in an emulator to see what they display.