I’m not to sure as I haven’t read the novel, but I saw a comment a while ago explaining the ending. Essentially Deon finds out the truth and learns about the deal between the Duke n the Demon King as well as the Duke making a fake excuse for Deon to attend the war. As well as discovering that the King didn’t do anything about it. Deon then goes on to kill the Demon King and the King (I’m not sure about the Duke). Deon I believe then prays(?) to the gods and they turn back time but it costs him his sight. So he goes back in time (I believe) but he’s blind.
Dayummmmm it just ends there?
Bro someone spoil what happens next