In the "art section" in Shun 2nd Edition Kanzenban (and maybe Shun 2nd edition on the PSX, but I don't have it), it lists what I assume are requirements for unlocking the various pictures. However, I don't speak Japanese and Google Translate doesn't work that well with low-res text. I've beaten both games on the cartridge so I just want to know what I have to do to unlock the rest of the art.
Found the answer on an archived 4chan thread.
http://i.imgur.com/0dY8mc1.png
Just to correct #20 in the illustration gallery list; the requirement for that one is to clear the pufferfish in field 54 blowing it away no more than twice.
Quotemaybe Shun 2nd edition on the PSX, but I don't have it
Just for the record, there's no DS-style art gallery in Shun, or Second Edition, on PSX.