Novels that has a plot where MC is an honest bloke and slowly steps to the path of no return (I mean being evil/psychotic/maniac or whatever you call it) because of some reasons that the author cooks up ~ It can happen in the start and middle of the story but not the end (cause there is no point to that except the afterword). It's also a plus if they explain the story of the MC why he changed if the story started that way.
https://www.novelupdates.com/series/the-man-standing-on-top-of-the-food-chain/ This one I think fits your description though it hasn't been translated for a while