An Original Dark Fantasy SI idea!
Okay... context first. So, this first started off waaaaay back when I had some ideas about the Familiar of Zero setting and thought to do some worldbuilding for it. I took Spellforce, an old RTS/RPG hybrid that I'm fond of, shifted the game mechanics a bit to translate better in Real Life physics, added in a dash of The Chronicles of the Black Company, mixed 'em all together, and... well, before I knew it, I had accidently created a world where I pretty much went, "You know what? Screw it, I'm just gonna make it an Original instead," and rolled with it.
So. Story idea.
Essentially, the Self Insert finds himself in control of a fantasy equivalent to a magical Brutally Efficient Self Replicating Machine of War, except the army it builds are more in line of a fanatic female Elven army than that of a machine. The thing is, the Self Insert is missing some blueprints, so he's literally running on Tier I, which his troops are well within a skilled, professional man's capabilities if better. He doesn't have access to either Tier II or Tier III, which are much more powerful and much more dangerous. Tier II is more of the line of the Nasuverse's Holy Grail War, except instead of employing Servants, it's armies of Servants, and Tier III, it's armies of Heroic Spirits.
Yes, now you understand why it is, indeed, a magical BESRMoW.
Unfortunately, the SI runs to a bit of trouble: none of his troops have magical capabilities, and what little they did have got destroyed when the local Orc guardians popped open the failsafe spell that sunk literally the only means the SI has to replace his troops, as well as the impossibly advanced magical runic infrastructure that would have made his life so much easier. Soon after that, he discovered that the elves are pretty much demonized by the local humans as magical powerhouses that would've genocided Humanity if their deity and his followers haven't done the same in the first place, and that the local magocracy government is hostile and is going to genocide him and his troops as well, as soon as they are able. Diplomacy is refused by lethal attacks upon their person.
So from Day Five, the SI has to deal with a hostile, established fedual magocracy whose out to genocide him and his soldiers with nothing but regular, medieval abilities, with no magical support, no gunpowder, no cavalry, and only infantry, missile troops, workers, and whatever else they can scavenge, while communicating orders by runners.
Literally the only things the SI has running for him are, A.) no need for food or water, and his troops just don't flat out tire out of fatigue; B.) superior equipment (the SI equipped his elves with Renaissance gears, or at least the closest approximation); C.) numbers (total was in the hundred thousand, which is really big for a medieval army, so he will pretty much outright dwarf his opponent); D.) surprise (took him five days to get a hundred thousand troops, in a medieval society; plus it will take time for the Empire to respond, and they already have troubles of their own.); E.) Organization and Loyalty; and F.) being damage soakers; his troops and him don't feel pain the same way, and they literally don't die unless you either chop them to pieces, or completely destroy the 'brain' analogue.
At first, the SI was able to overrun the local regional forces and install pseudo-government. Most of the time he is either dealing with politics, putting down riots and rebellions, or trying to keep everything under control, while also trying to figure out why he's here, what the heck is going on, and why does everyone hate him so much, I mean seriously?!!
And then the first, real Imperial response comes. And it's lead by Goddamned Magical Girls, who sprout flowery, colorful nonsense about Love, Justice, and the Empire, and then proceeds to wreck his shit, Bloody Hell!
So begins of trying not to get him and his troops from dying from Sparkly Magical Bullshit(TM).
War. War never changes.
