The Rust Syndicate's headquarters' description on the map is that "its design was based on a far-off region". What is the region?
The only thing I noticed is that the start of music when you enter sounds a lot like the Festival of Masks in Kitikami (flutes and rattly percussion), but it then changes to a more brassy tune, so I have no idea.
The best I can find is Johto. The entire group is based off Yakuza (Japanese mafia, to be simple) Specifically, their logo looks to resemble Yamaguchi-gumi, which origins can be found in Kobe, in Kansai (where Johto is based off)
https://en.wikipedia.org/wiki/Yamaguchi-gumi