If the game fails to save on modern systems like Windows 10, try removing the Read-Only attribute from the Documents\KOEI folders or allowing the game through Windows Controlled Folder Access settings.

xcopy "C:\Users\%USERNAME%\Documents\Koei\Dynasty Warriors 4 Hyper\Savedata\savedata.dat" "D:\DW4_Backups\" /Y echo Backup completed on %date% %time% >> D:\DW4_Backups\backup_log.txt

If you have placed a save file in the folder but the game doesn't recognize it, or if your game simply won't save your progress, try the following fixes: