"Isekai" is not a genre and should being referred to as such.

Isekai simply means "another world". It doesn't say what kind of world it is. It could be a fantasy world, a steampunk world, a sci-fi world, anything.

Fantasy worlds and harems aren't staples of "Isekai", that only applies to a few popular examples and their copycats. Nothing about "Isekai" requires it to be a fantasy world or for there to be a harem, most of them don't.

If the defining traits of a "genre" aren't actually requirements for it, but just something authors do because they're lazy, wants to cash in on a trend, or were inspired by another work that had those things, it's not actually a genre.

It's a genre though

>>281222001 (OP)
Isekai is just the English word used when discussing なろう系 media.

>it's another poster who is too midwit to realize he means to say jfantasy
>"look, I found another Japanese element in this show made in Japan. How can this be?!"

>>281222001 (OP)
>noun
>A category of artistic composition, as in music or literature, marked by a distinctive style, form, or content.
Isekai is written by LLMs prompted by hikikomori whose literary input are the same video games, so it has a distinct style.
In isekai the same events happen (the protagonist is rezzed, they learn about the skill system, they progress through guild tiers, etc) so it has the same form.
Isekai is populated by characters so identical that they are referred to by tropes (the hero, the demon king, the villainess, etc) instead of names, so it has the same content.