You mean in terms of general events? 'Cause a fuck ton of the specifics are different, right? Harold wasn't originally one of the 3 black robes or wtv iirc.
O . o?
From what what i remember,
he was the third person in the webnovel.
Yes there are differences between the events protrayed in the story and the original game. But major points are consistent no matter how much Harold tries to subvert them.
He is still engaged to a FMC, despite numerous attempts to get it broken off. He is dubbed a traitor despite saving his entire squad and he was railroaded so hard in the military tribunal it was surprising the judges were not freight trains, the numerous missions that he is forced to go on for Justice, and the most egregious example is his enforced speech patterns and even some physical actions.
Harold has some wiggleroom to affect some changes to his fate, but he is mostly forced to play the part of the game's villian. And that requires he be in certain places and say the appropriate lines.