Another World (異世界, Isekai) is a theme present in Japanese anime, manga and other media. It usually has to do with the main character being transported to another world, hence the name. Other worlds regard to parallel fictional universes or virtual worlds, unbeknownst to the protagonist of others around him/her.
The theme can be characterized as wish fulfillment, with the person being transported often being a NEET, hikikomori, gamer, or just a regular human. In the new fantasy world, they are able to succeed through their comparatively unimportant-in-real-life genre knowledge or other skills. In some cases like Isekai wa Smartphone to Tomo ni, their power can range from tremendous magical abilities surpassing anyone else, to relatively weak, as in Re:Zero − Starting Life in Another World, where the protagonist does not gain any special power beyond the ability to survive death in a type of temporal loop.
In general, the "isekai" protagonist is usually regarded as the "chosen hero". But some titles subvert the theme such as Drifters, where people entering the other world are historical generals and other warriors who are more brutal than the world's inhabitants themselves. Titles like Tensei shitara Slime Datta Ken, the protagonist starts off as non-human as a weak blob. Some stories involve people being reincarnated as unusual inanimate objects, like a magical onsen.
In earlier times, the genre started with titles like El-Hazard and Fushigi Yûgi, in which the protagonists retained their original appearance upon entering a different world. Later titles such as Yōjo Senki inverse the genre where the protagonist dies and reincarnates in a different world, such as Knight's & Magic, with the latter retaining their memories and interests from their previous life.
The .hack franchise was one of the first to present the concept of isekai as an actual virtual world, with Sword Art Online following in its footsteps.
|El-Hazard||Tensei shitara Ken deshita||Isekai wa Smartphone to Tomo ni||Sword Art Online||Gate: Jieitai Kanochi nite, Kaku Tatakaeri|
|Fushigi Yūgi||Isekai Yakkyoku||Kono Subarashii Sekai ni Shukufuku wo!||Gundam Build Divers||Out Breack Company|
|Dog Days||Knight's & Magic||Restaurant to Another World||Accel World||No Game No Life|
|Mashin Hero Wataru||Yōjo Senki||Re:Zero − Starting Life in Another World||Log Horizon||Hyaruken no Valkyria|
|Isekai no Seikishi Monogatari||Legend (TAKANO Masaharu)||Isekai Izakaya "Nobu"||Overlord||Hataraku Maou-sama|
|Isekai Maō to Shōkan Shōjo no Dorei Majutsu||Exterminator||Saving 80, 000 Gold Coins in the Different World for My Old Age||Arafoo Kenja no Isekai Seikatsu Nikki||Isekai Quartet|
|Tensei Kenja no Isekai Raifu ~Daini no Shokugyo wo Ete, Sekai Saikyou ni Narimashita~||Kamitachi ni Hirowareta Otoko||Magi Craft Meister||Manuke na FPS Player ga Isekai e Ochita Baai|
|Seijo no Maryoku wa Bannou desu||Tensei Ouji wa Daraketai||Maou-sama Retry||Death March kara Hajimaru Isekai Kyousoukyoku|
|Tate no yuusha no Nariagi||Isekai Nonbiri Nouka|
|Isekai Cheat Magician||Isekai Yakkyoku|
|Zero no Tsukamai||Yondome wa Iyana Shi Zokusei Majutsushi|
|Arifureta||Kenja no mago||Caturikun|