The use of the .rar format itself is a nod to that era's technical constraints. RAR offered better compression and "recovery records" compared to early ZIP files, which was vital when downloading large image sets over unstable DSL or dial-up connections. If one "byte" was corrupted during the hours-long download, the RAR format often allowed the user to repair the file rather than starting over.
: Unlike modern compressed web images, these RARs often contain raw or minimally compressed BMP/JPG files intended to preserve the print quality of the original physical media.
: The specific alphanumeric string suggests it was part of a much larger, systematic project by a release group (such as those found on Winny, Share, or early 2-channel boards) to digitize entire libraries of Japanese idol culture. The Cultural Context of the RAR