Edit: apparently this is a very common form of Japanese storytelling called an isekai. There are 8 billion people in this world, no idea can be original. And sometimes you miss out on things many other people know. I’m clearly one of today’s lucky 10000.
Isekai harems are “all of the above.”
Hey sometimes they are flat chested autistic girls or 7,000-year-old dragons who happen to look like a 9-year-old.
Personally I’m interested in neither but I’ve read a lot of manga