Isekai

Isekai (Japanese: 異世界) (lit. "different world") is a subgenre of Japanese fantasy light novels, manga, anime, and video games revolving around a normal person being transported to or trapped in a parallel universe. Often, this universe already exists in the protagonist's world as a fictional universe, but it may also be unknown to them. The new universe can be an entirely different world where only the protagonist has any memory of their former life, as in Saga of Tanya the Evil, or one that they reincarnate in. It may also be one where a formerly virtual world turns into a real one, such as in Log Horizon and Overlord.

Characteristic
The subgenre can be characterized as wish fulfillment, with the person being transported often being a NEET, hikikomori, or gamer. In the new fantasy world, they are able to succeed through use of their comparatively unimportant-in-real-life genre knowledge, or gaming skills through the use of a game interface only they can access. Their power can range from tremendous magical abilities surpassing anyone else, as in In Another World With My Smartphone, to relatively weak, as in Re:Zero, where the protagonist does not gain any special power beyond the ability to survive death in a type of temporal loop.

While the protagonist of an isekai work is usually a "chosen hero", the genre was also subverted by Drifters, where the people entering the fantasy world are historical generals and other warriors who are more brutal than the inhabitants of the world themselves, and in That Time I Got Reincarnated as a Slime, where the protagonist starts as a weak bloblike monster rather than a human. Some stories involve people being reincarnated as unusual inanimate objects, like a magical onsen.

History
Early titles that could be called isekai include El-Hazard and Fushigi Yûgi, in which the protagonists stayed similar to their original appearance upon entering a different world.[1] Later titles such as Saga of Tanya the Evil and Knight's & Magic involved their protagonists dying and being reincarnated in a different world.

The .hack franchise was one of the first to present the concept of isekai as actual virtual world, with Sword Art Online following in its footsteps.

The genre became so popular that in 2016, a Japanese short story contest banned any isekai entries. The publisher Kadokawa banned isekai stories as well in their own anime-style novel contest in 2017.