he has to change the story in order to survive but believes the story can't change in fundamental ways. You can't believe that AND want to live in the way these stories are set up. At best you get a meandering and indecisive MC that just gets pushed around by events.
Most stories solve this by having MC realize too many things have changed and they must become proactive, but this MC hasn't really changed that much since the beginning.
not too much necesarily. Only thing he has to change is his fate, so that the world doesn't collapse. If he can survive the encounter with the hero party or somehow even join them down the line, then his survival and their success is practically guaranteed. However, for the hero party to get to that point, they have to go through certain challanges. And while you COULD take a risk and try to change the story in a potentially more favourable direction, you loose a great portion of your advantage against your enemy. Thus, it makes more sense to nudge the story in the intended direction, while trying to tweak it in order to prevent as much harm as possible. Now this would mean that he would have a high chance of dying. This, of course, is and important thing to consider when you are in his shoes. You wouldn't want to die, if you didn't need to afterall. However, if you die, then that would signify the fact that the story is going roughly according to the original, which would most likely lead to the survival of most people. This is the exact line of thought he has had throughout the whole story. The reason he is trying to push everyone away, while propping up the protagonist's party is that even in the worst case, he wouldn't drag anyone down with him.
As you've mentioned, there are rather few ways to change the actions of an MC with this mindset.
The first way you can change them, which I doubt will happen here, is to show the MC that their plans of staying loyal to the story will not work. Be that through careless actions the MC committed leading to big divergence, or through some form of clairvoyance, where MC is shown it failing (I have not actually seen a story like this, but it would be possible and could be very interesting if pulled off, as it could lead to a mental breakdown of the MC like "It wont work?? Then what have I been doing up to now?! Has everything been for naught??!!" Sorry for the side tangent).
The second way you can change them, is by having them develop strong feelings for certain characters. This is most often done through love, but could also be done through familial bonds as well. The crux of this method is to get the MC to a point where they can no longer ignore their feelings and basicly go "fucck it, whatever happens, I'll tackle it head on, even if it is the objectively worse decision, I refuse to follow the story any longer." I believe that this is the more likely thing to happen. However, I don't expect to see this development until much further in the story.
I personally don't mind much that he will keep this way of thought for some time still, as I believe him to be proactive enough even with it. This so far has avoided the trap of having the MC become a passanger in their own story. Many times the MCs of such stories just go along with the story, letting the events happen and then trying, in vain, to act like their character. Here however, MC is actively hindered in his plans by his mouth. He has, after all, prevented many deaths in the Sumeragi estate, lessened the burden on the citizens of his territory, brought about agricultural change at least a decade before it should have started, participated in the tournament, joined the knights early, prevented a mass slaughter in the forest and has brought one of the heroparty members to the main antagonist so that the girl could learn from them. And we know little enough, about the actual story he is trying to follow, that these actions seem meaningful. They may not actually be too meaningfull depending on what the author has in mindfor the future of "the plot", but to us, they seem like major changes, which pushes the idea that the MC is an active participant of the story, rather than a passenger.
Of course I understand your problems with it. I would also prefer it, if the author could have written a story, with less tropes in it. Afterall, tropes can get very repetitive and boring. However I do believe that this is an above average story in it's categories. Characters, with the exception of their acceptance of MCs speech sometimes, seem rather human with completely understandable arcs. Worldbuilding is fine and while it is very subjective, but MC seems like the best "Oh, the guy I possesed influnces my speech to sound villainous." character I've seen. Which doesn't mean much, as the concept can only go as far as a 7/10 (good), but still. It doesn't drag down the story much.
Sorry for the giant essay, I just found this interestign and wanted to have a bit of a discussion.
