I think it would be better to just make a medieval sort of X-com than a story about a single character. You don't play as an heir, you play as a special order of X-com style knights put together to deal with a supernatural threat (typical fantasy monsters, goblins, vampires, dragons, etc.), and you're funded by different kingdoms and regions. You build up your order making bases upgrading from forts to castles. and you respond to reports of strange phenomena, learning about the creatures and their powers similar to X-com's technology research, but with sages or monks to research. And then discover that the ultimate threat is a portal or something in a wizards tower or on an island. Then you have to build a special boat, or research a way to get into the wizards tower to go through the portal for the final battle with other worldly creatures to close the portal and return the world to normal. Instead of a psionics lab, you could build a monastery in your base for some kind of religious training for mind defense, and to use holy relics like crosses vs. the vampires and ghosts and such. But you could still research the use of garlic, mirrors, and wooden stakes without the monastery. So it could be sort of like ghostbusters with medieval knights. But yeah, the geoscape would probably be better as a flat map in that type of game.
