It contains a segment of the game's data. You cannot install or run the game using only "part3.rar"; you must have all parts (e.g., part1 through partX) in the same folder to extract them.
Old versions of WinRAR or 7-Zip have known security flaws that can be exploited by malicious archives. Toukiden.Kiwami.part3.rar
Use an antivirus or upload the file to VirusTotal to check for hidden threats. It contains a segment of the game's data