I've had a go at using the debugger to see what I can find out, I'm no expert on this sort of thing though
The intro text is a texture image, 512x256 pixels. It's not a font file, but CLUT4 ABGR image containing a literal list of all the lines that appear in the intro. It'd internal ID is 0x040d0000, though at the moment I'm still uncertain which file contains it.
The Japanese text in the rectangular box is a transparent graphic (the box is a separate texture) similar to the above in that it says what it needs to in the image file itself. The file is 256x128 and only appears to contain one single line of text, it's internal ID is 0x040f8000 and the image format is the same as the intro text. Again, I'm unsure of which file this graphic uses.
I had a theory that if I could export those two textures from the debugger it might make it easier to locate them within the files, it won't be quite that easy, but there's a base memory address for both that may make it possible for me to extract the raw data straight from the PSP's RAM to see if I can find the same data within the ISO, can't promise anything though.
Ah.. a start: I've narrowed the second image down to being in DATA.DAT - now to try and extract that file to narrow it down further. It's actually compressed within the file - the memory dump has lots of zero bytes which aren't present in DATA.DAT, though non-zero byte sequences can be found identical in both files. Perhaps the compression only affects long sequences of zeros?