Another popular story, in the same genre ('Isekai'), which should also get an anime,'Kumo Desu Ga, Nani Ka?' (high school class becomes heroic princes and princesses.our hero, friendless gamer-girl becomes mook tier monster in a dungeon) eventually deals quite well with the often ignored question of why a real-seeming World would so closely resemble a game.

When the game was copied, it was copied complete with the popular dungeons, like Nazarick. Maybe when the Wild Magic event that created the currently popular forms of magic occurred, it copied the rules for how the system of spells would work from a computer game on a different World. On the other hand, maybe it is all just magic. If he were still thinking using his human brain, back in his apartment, he would have passed out from low loos sugar and lack of sleep days before he even goes outside for his fateful Moonlight talk with Demugure. Momonga could have been sitting, as lifeless data on a hard drive, along with the rest of Nazerick, for all the years it took for true AI to come into being, finally, after loads of history takes place, often using rules that came into being long after Momonga was recorded, the Great Tomb is awakened and the Supreme One orders Sabas to scout the perimeter. Also, there is mounting evidence.we even see plenty of it in the anime, that there have been other players in the new World.many, many years ago. That is a great answer! It also explains so many other things, for example, the new setting appears to run on many of the same basic rules.with new options added, like marshal arts (and rune magic) that didn't exist (or weren't implemented, or were largely unknown to the players), in Yggdrasil. Why bother with the far future? Why the differences he has noticed in his emotional make-up? My theory? He isn't 'real'. The Momonga we see in the new world (new game) is an AI version of that player. You can check with the overlord community on reddit and it is common understanding that Ainz is in a real world. There is one which is some time after the game ended with a few of Ainz old guild mates talking in real life and some other details. Not only is there a Light Novel, but there are a lot of secondary or mini Arcs that have other details. There are some other parts that explain this a lot better than I can. NPC and people show human emotions, fears, world history and other complex matters which are hard to explain in a game world.Ainz was in the New world for a long time, he would have died already.(Ainz wasn't very known and didn't have many friends in real life, no one would have checked on him).It is mentioned that there are laws against stimulating senses in games.There are some hints as this in the beginning of the light novel that leads you to believe that it isn't like SAO. Ainz was transported to a new world, some say he was transported because of wild magic, but the wild magic for some reason believed his avatar was his real body.

Animes like overlord