Splitting Image takes place in the Four Winds Kingdom (or just Aeolia), a world enclosed by a cylindrical barrier. It consists of four floating islands, vertically miles apart, with slightly different climates, but all overall a bit cold. Standing on the top one, Boreas, is like being in the top of the world, while standing in the bottom, Eurus, is like sitting under a shattered mountain.
Fantasy creatures of many types live in Aeolia, usually in harmony, in the surviving hamlets, villages and towns. Though the world is in our equivalent of late medieval ages and start of renaissance, magic permeates every aspect of it, and much technology is replaced by spells and abilities. Dragons act as sentient transportation, elves can synchronise earth and nature spells to raise a beautiful house, an orc can travel with a clear head as a small crystal can carry a whole jar of water.
Aeolians survive and celebrate when they can, because both lives and material gain can be cut quite short in this realm. Animals can also cast magic, and this makes forests and jungles homes for extremely dangerous beasts that don't always stick to the wilderness; many artifacts of unknown power, from ages forgotten, can be misused and cause untold damage in the wrong hands; and every few decades, a new Dark Lord rises to cause random destruction, raze villages, seemingly do everything in their power to make the people most desperate... And eventually, the fell sorcerer dies, and the kingdom has a few more years to deal with only their usual dangers.
One didn't do that however. Their last Dark Lord was laser focused on stealing objects of power, and while that also meant a lot of houses and temples in many pieces in his wake, he always made sure to never kill. An idiot, really, that seemed to have endless potential, but always easily thwarted over little mistakes, oversights, or just simply underestimating his opponents... Until he made a mistake that no one could fix, and instead of dying, persevered on, more for others than himself.
That's Mortimer, our protagonist.
Honestly, it's a LOT of inspirations for this world. I can name off the top of my head Touhou for being a potluck of fantasy creatures, Xiaolin Showdown for the saturday morning cartoon structure with a ton of special artifacts littered across the world, Final Fantasy XII for the floating island of Bjhuerba + Skylanders for the whole place, that made me love islands that defy gravity way too much. This is all part of a much larger world with different localized inspirations, but it's quite the odd one on its own.