I present the real OG of Isekai…
A Connecticut Yankee in King Arthur’s Court written in 1889 by American author Mark Twain.
Which has multiple film and TV adaptions. Such as Walt Disney’s A Kid in King Arthur’s Court.
Not the 1865 Alice’s Adventures in Wonderland which also has the same credentials but, as you can see, is earlier?
Still not sold on calling all of it Isekai regardless, but at least check your own facts
I feel like a fantasy world that you can semi-freely travel to without death is not isekai.
I mean, Inuyasha exists.
Which is not an isekai, so…
Uh, the main character Kagome falls through a well into feudal era Japan and cannot get back.
Not sure how that doesn’t qualify as an Isekai.
She goes back and forth a lot tho.
After a huge amount of time, she’s stuck there for a while.