Go DmC Devil May Cry\DevilGame\Config and open the file named "DefaultInput.ini"
Then find [Engine.PlayerInput],
And postscript following sentences.
↓
Bindings=(Name="F9",Command="slomo 1", bPrimaryBinding=True)
Bindings=(Name="F10",Command="slomo 1.2", bPrimaryBinding=True)
After that, you...