If you found this file on a third-party site, be cautious. ZIP files from unofficial sources can be used to mask malware. Only files downloaded directly from the official DLsite store are guaranteed to be safe and support the original creators.
The code is the unique product identifier used by DLsite. This specific work is part of the "Ear Massage" or "ASMR" category, which is popular for relaxation and sleep aid. RJ304054.zip
Approximately 1GB to 2GB depending on the audio quality chosen at download (WAV vs. MP3). If you found this file on a third-party site, be cautious