The author like a number of others chooses to pack up their content into rpa archive files. Sometimes you will just see something like an archive.rpa file sitting out in the game directory with little else. Other times you may see a number of archives such as images.rpa and scripts.rpa as the author breaks up content by category.
I use a tool called rpatool from Github which can be downloaded
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When the authors have also removed the Renpy source and just left rpyc bytecode files only I use another Github project
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to recreate the sources that can be edited. The result is a line for line decompile that preserves the original variable names but only has empty lines where comments originally appeared.
I only see rpa archives as an attempt by authors to "hide" the content from prying eyes. Some might argue that they can increase performance by only having a single open file handle, but it's not like we are using them like a Linux shared library or Windows DLL file. They don't seem to make any attempt to use compression to reduce file size, and besides, most Renpy content in the form of video and images has already been compressed in the first place.