Isekai

Isekai is a Japanese fiction genre in which a protagonist is transported to, reincarnated in, or trapped in another world, often one governed by unfamiliar rules.

Portal fantasy: Fantasy in which characters travel from their familiar world into a fantastical one. Isekai often uses this broader structure, though reincarnation and entrapment can replace a portal.
Portal fiction: Stories organized around passage between distinct worlds through a doorway, object, or other threshold. A portal can make the protagonist's crossing into an isekai world immediate and visible.
Urashima Tarō: A Japanese folktale about a fisherman who visits an underwater palace and returns to a changed world. Its journey beyond ordinary life offers an early Japanese parallel to crossing into another realm.
Mushoku Tensei: Jobless Reincarnation: A Japanese light novel series about a middle-aged shut-in reincarnated as a child in a fantasy world. Its long life-spanning plot became a prominent model for reincarnation-centered isekai.
Reverse isekai: A fantasy premise in which a being from another world enters and lives in the contemporary human world. It reverses the usual direction of travel, bringing the otherworldly figure to Japan or another familiar setting.
Reincarnation: The rebirth of a person or soul in a new body or life. Many stories begin when a protagonist dies and starts a new life in another world.
Reincarnation fantasy: Fantasy in which a character is reborn, often retaining memories or identity from a previous life. This isekai mode gives the protagonist a new body and sometimes knowledge from a former life.
The Tale of the Bamboo Cutter: A Japanese folktale about a girl from the Moon who is found and raised on Earth. Its otherworldly origin and eventual return anticipate themes later used in Japanese fantasy.
Re:Zero − Starting Life in Another World: A Japanese light novel series about a young man transported to a fantasy world who returns after death. Its repeated deaths turn a familiar arrival premise into a story of costly persistence.
Sword and sorcery: A fantasy subgenre centered on personal adventure, magic, and martial conflict. It can share isekai's settings and action while keeping its heroes native to the fantasy world.

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