In the early 2000s, before legal streaming was robust, fans who owned the physical discs would them to MP3s, compile every single A-side and B-side in chronological order, and compress the folder into a .RAR (a common archive format) to share on peer-to-peer networks, forums, or blogs. The phrase "Complete Single Collection rar" became a search query whispered among indie J-rock fans desperate to hear every note the band recorded outside their albums.
I believe you're referring to the Japanese rock band Blankey Jet City, and you're looking for information on their complete single collection in RAR format. Here's what I found:
Blankey Jet City's Complete Single Collection "Singles" is a comprehensive 20-track compilation released on March 27, 2013 Universal Music Japan
Blankey Jet City Songs, Albums, Reviews, Bio &... - AllMusic