Help unpacking Arc file from obscure PSP game (Mimana-Iyar Chronicles)

[discPistol]

Hey guys, I'm pretty new to modding, and using quickbms. Sorry if this is a rookie question. I'm trying to extract the sprites from an old PSP game (Mimana-Iyar Chronicles), which I have as an iso. I am able to unpack the iso, which extracts to a few folders.
PSP_Game/SYSDIR
PSP_Game/USDIR
in the USDIR folder, we have the biggest file in the lot, an Arc called pa.arc. I'm guessing this is where to look for assets. But I can't seem to extract from it. I've tried a few different unpackers, but nothing seems to work. I think it's some sort of proprietary compression. Any suggestions would be appreciated!

thanks yall,
-disc

[aluigi]

It may be a known format but we need the file for analysis.
You can use the following script for generating two files from that big one, zip and upload them so we can check the content:
http://aluigi.org/bms/filecutter.bms

[swosho]

IIRC this script also works with Mimana Iyar Chronicle: http://aluigi.altervista.org/bms/naruto_paa_bin_arc.bms