To invert the y-axis of the mouse, you need to enable a hidden entry in the settings file of the game.

1. Make sure that X-Blades is not running. If it is, then close the game.
2. Open Notepad or any other text editor.
3. Hit Ctrl+O to open a file.
4. Enter "%LOCALAPPDATA%\XBlades\settings.blk" (without the quotation marks) into the address field and hit enter to open the file.
5. Scroll down and near the end of the file you should see a line that reads "controls{".
6. Immediately after this line, insert a new line that reads "invertMouse:b=yes" (without the quotation marks).
7. Hit Ctrl+S to save the file and close Notepad.

Next time you start the game, the mouse y-axis will be inverted.