From Mizuumi Wiki
How To Configure Keyboard Controls
Some people do not have a USB game controller to use for this game, in this case you will have to do a little more work to configure your controls.
- First locate your user profile folder, it will have the same name as the account you log in to your computer with. (Mine is C:\Users\ACCOUNT_NAME)
- Go to the folder C:\Users\ACCOUNT_NAME\AppData\Roaming\PDWHOTAPEN\yatagarasu_ver20121231 (You will have to enable "Show Hidden Files And Folders" in order to see AppData.)
- Right-click on Gd.lst and either Edit or Open With and open this file with Notepad.
- Find the line [KEYBOARDCONFIG0] and change the values accordingly.
If you need help, this is a useful reference. Oops looks like OEM keys don't work!