Genres
Portal fantasy
The older Western category of travel between worlds: Narnia, Barsoom. The crossing is the obligatory beat.
Portal fantasy is the Western category of fiction built on travel between worlds, predating isekai by decades: Narnia and Barsoom are the canonical early examples. There is no enforced game-mechanic or reincarnation requirement; the crossing itself is the obligatory beat.
Genre references deliberately decline to draw a hard line between portal fantasy and isekai, treating them as closely related, overlapping traditions. Writers choosing platform tags should know both labels exist and describe the same story skeleton with different cultural framing.