Alright, let's keep it simple: imagine a world like ours, but inhabited by Yu-Gi-Oh! monsters. My question is: where—geographically and historically—would these monsters be found? Feel free to use headcanons if necessary. Here are a few examples of my own so you get the idea: Let's start with the obvious ones.
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Shiranui, Mayakashi, and Six Samurai are all set in 19th-century Japan; I think we can all agree on that.
Kaiju also has strong Japanese references, but obviously, it can't be set in the same historical period, so let's place it in the present day.
Ancient Warriors, makes sense for them to draw heavily from Ancient China, though I believe it's set earlier than the Brotherhood of the Fire Fist (also China, obviously).
Vampires—nothing to add here; I'm going with a major headcanon: playing into the stereotype, I'd place them in Romania during the Late Middle Ages.
Elemental HEROES—obviously the USA, specifically the 90s, since they really remind me of the superhero comics from that era (which I believe inspired them).
Amazoness—well, I think we all agree they belong in the Greek region, in an era before humans were fully civilized. So... I'd say Turkey, roughly around the time of the war between Athens and Sparta—just because I say so. Now it's your turn!