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 from Earth being transported to, reborn 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.
In a Reverse Isekai, fantasy characters are transported from their respective worlds and/or are forced to assimilate into modern society, such as The Devil Is a Part-Timer!
The subgenre can be characterized as wish fulfillment, with the person being transported often being a NEET, shut-in, or gamer (as in No Game No Life). 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 bloblike monster with special abilities rather than a human. Some stories involve people being reincarnated as unusual inanimate objects, like a magical onsen.
The concept has origins in ancient Japanese literature, particularly the story of Urashima Tarō, a widely known folk tale in Japan that isekai writers grew up with. It is about the fisherman Urashima Tarō, who saves a turtle and is brought to a wondrous undersea kingdom, but the story later has a twist (after spending what he believed to be 4-5 days there, he returns to his home village only to find himself 300 years in the future). Several later examples from English literature include the novel Alice's Adventures in Wonderland (1865), as well as The Wonderful Wizard of Oz (1900), Peter Pan (1902) and The Chronicles of Narnia (1950).
Early anime and manga titles that could be classified as isekai include Fushigi Yûgi (1992 debut) and El-Hazard (1995 debut), in which the protagonists stayed similar to their original appearance upon entering a different world. Other 1990s titles identified as isekai include the novel and anime series The Twelve Kingdoms (1992 debut) and Magic Knight Rayearth (1993 debut). The anime film Spirited Away (2002) was the first world-wide known isekai anime film, although the term "isekai" was not commonly used at the time.
The .hack franchise (2002 debut) was one of the first to present the concept of isekai as an actual virtual world, with Sword Art Online (2002 debut) following in its footsteps. A popular isekai light novel and anime series in the 2000s was Zero no Tsukaima, where the male lead Saito is from modern Japan and is summoned to a fantasy world by the female lead Louise.
The genre eventually 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/manga-style novel contest in 2017.
In 2017, Goo Ranking conducted a poll in Japan asking people to name their favourite isekai anime. The top ten were Spirited Away, Pop in Q, Sword Art Online, Magic Knight Rayearth, Re:Zero, The Twelve Kingdoms, KonoSuba, World Trigger, Kyo Kara Maoh and Gate.
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