Based on its format, this appears to be related to (a Japanese adult video platform) and includes what might be a split archive part ( .part10.rar ).
: This refers to the "Pay-Per-View" section of FC2, a popular Japanese media hosting site where independent creators upload content. 3620789 : This is the unique content ID number.
Right-click only the first part ( part01.rar or sometimes 001 ) and select "Extract Here." The software will automatically read the subsequent parts—including part10rar —and combine them into a single, usable video file. Safety and Digital Etiquette