Hey guys. An idea. For something. So let's pretend that, the SI has your standard powers. Let's say that your SI has your standard competence. Now plop him in the middle of a podunk little village. Maybe a town that's got hit by drought or something. So then, uplift, upgrade, crafting infrastructure with magic and stuff, trying to make it into a working civilization. So... in the end, it becomes a city state.
So then people hear about the city, and then start taking notes. Some protest this. Saying that their secrets will be stolen. Some advocate that they be executed as spies. Some say that, with their power, infrastructure and numbers, they should go forth and conquer other cities.
So in the end, the isekai realizes that, yes, the world outside is pretty goddamned shitty. Crime. War. Injustice. Poverty. Famine. Disease. Plague. Roaming bands of monsters. So he decides.. that he needs to change things. Not by conquering others, cause that's dumb. But by being a source of good.
First he makes a border. All within the border, are citizens forever more. No slaves. All citizens. All will answer to him. Second, each time there is a plague, famine, or natural disaster, he sends people over to help. And each time, he offers to help out others. To let them join. So slowly, ever so slowy, the state grows. No conquest, but its just that people can legitimately see that his state is better run, more advanced, and generally safer.
Of course, there's more to this story. I think I should make it so that he's got a shortage of charisma, so he doesn't really try to do insanely stupid things like convince kings to abdicate or step down. Or has difficulty comprehending the sheer difficulty and poverty of the time he's in. Like, for example, wondering why they don't use metal for their ploughs... then realizing they couldn't afford it. Or chasing after a girl who's been taken by the local lord as a mistress to get her back by force, only for the girl to scream at him because she's finally not hungry and has clothes and a soft bed and how dare he try and ruin her chance to move up in the world? Or, say, wondering why it was such a big deal to ask for more food or extra clothes. Not realizing the drought has come and that peasants don't really have clothes anyway.
Or trying to deal with religion. And that. Yes, these people are dead serious about religion. And yes, they really think that. And yes, you're an atheist, but don't rub it in their faces, because you don't know what they'll do. Or trying to enforce religious harmony, when its a problem, cause of blood feuds, religious persecution, and good old 'burn the infidels'.
Or try to write about how the people deal with it. How does one adjust their way of life, after a drought? How does one's perspective change, after you have someone capable of conjuring water and food, and commanding the weather, on your side? How does one change, when he starts producing aspirin, antibiotics, birth control, antiseptics, and every other modern medicine? How about when he starts talking about setting up a legal system where all are equal under it. How about when he starts talking about things like 'no slaves'?