sigh, this is always something I just see as so lazy from japanese isekai authors. They make a Japanese like warrior country in the new world (always an outlier in the world, never like 70% of the culture), they always dress and act just like medieval Japan. Usually same building styles. And almost always a far east country.
At least there's some reason for some countries of the new world if they gets Isekai visitors from our world sometimes, and then sure, outsized impact from a cheat existence. But otherwise, random bits of standard fantasy / magic version of our world, and bam, standard Japan out of nowhere. Like, have dwarves wear kimonos. Elves use Katanas. Birdmen have pagodas. Almost the whole world uses mostly Japanese culture and only 1 small country is European. etc etc. Don't just group everything into one small (probably island) country, it's like a self-insert power fantasy country in a self-instert power fantasy MC Isekai otherwise.