This is the first file ( .part01 ) of a compressed game installation package. FitGirl Repacks are known for highly compressing games to make download sizes smaller.
You need file archiver software like WinRAR or 7-Zip to extract the contents. Demon Slayer -- fitgirl-repacks.site --.part01.rar
Place all downloaded .rar parts into the same folder, right-click on ...part01.rar , and select "Extract Here." The software will automatically combine all parts into the game installer. This is the first file (