Well, I've managed to build like 80% of Eustia, but it really took me a while to figure out:
The initial unpacking part is missing. One's on your own to unpack BGI arc files. I've managed to do it using "Ethornell" module of ExtractData.
Image conversion part is missing. You have generated pngs somehow, I'm still at loss how to do that.
Whole extracted.d / extracted.s stuff is very confusing - I have no idea which is which and there's no documentation.
BGI2STORY works, but it requires one to manually compile your .ksy format description files first
... and now that's a very untrivial matter, as it means that one has to find Kaitai Struct project, install it, and figure out that you need to run "ksc -t ruby file.ksy" to compile .ksy => .rb
Noratoto port is much better documented, and, thanks to that, I've managed to get through everything, besides .png conversion. Thanks for your impressive work, but it's still *way* beyond being user-friendly or anything.