Recently, works featuring protagonists who are transported or reincarnated from the real world into fantasy realms where they wield magical or overpowered abilities have gained widespread popularity. Multiple titles air each season, solidifying Isekai as a major genre in anime.

In this article, we delve into the roots of the ever-popular Isekai genre in Japan, explore its evolution over time and its fusion with other genres, and highlight some of its most iconic works, based on our editorial team’s insights.

What This Article Covers
・The roots of Isekai anime
・Major distinctions between "Isekai Reincarnation" and "Isekai Transition"
・Popularity and the background of the boom
・The evolution of Isekai over time and across genres
・The triggers behind the boom
・Recommended Isekai anime and manga

What is Isekai?

"Isekai" is a major genre in Japanese fiction, particularly in light novels, manga, and anime. It features stories where modern-day characters are reincarnated, transported, or summoned to another world filled with magical or fantasy elements, different from the real world. This genre has garnered widespread popularity, with various expressions such as "Isekai," "Reincarnation Isekai," and more, leading to further subgenre divisions.

Many readers of this article might associate "Isekai" with titles like That Time I Got Reincarnated as a Slime or Sword Art Online. These works incorporate RPG elements similar to Japan’s Dragon Quest and Final Fantasy.

The question, "What was the pioneering work of the Isekai genre?" is likely one that piques the curiosity of many. How, then, did the concept of Isekai evolve and develop in Japan?

Early Isekai Works
The origins of Isekai as a literary genre can be traced back to Western fantasy. Notable examples include Mark Twain's A Connecticut Yankee in King Arthur’s Court (1889) and C.S. Lewis’s The Chronicles of Narnia(1950). These works involve modern characters traveling to different times or worlds, using their contemporary knowledge and skills to navigate their new surroundings. Going further back, Alice’s Adventures in Wonderland (1865) is another example.

This kind of setting was also adopted in Michael Ende’s The Neverending Story (1979), where it became a universal genre used to depict human psychological growth.

Isekai in Japan
The pioneer of Isekai in Japan is considered to be Warrior from Another World(1979) by Haruka Takachiho, known for Crusher Joe and Dirty Pair. It tells the story of a high school student who embarks on an adventure in another world. Subsequently, Fuyumi Ono’s The Twelve Kingdoms series, which began in 1992, gained widespread popularity, further expanding the Isekai genre. This work also features a high school protagonist, establishing the genre’s appeal among young adult readers. Around this time, several other Isekai works emerged in anime and manga.

However, the modern surge in Isekai releases was significantly influenced by the success of The Familiar of Zero (2004) by scriptwriter Noboru Yamaguchi. The explosive increase in fanfiction submissions on the Japanese novel posting site "Shōsetsuka ni Narō" helped establish Isekai as a major genre.

Isekai Reincarnation and Isekai Transition

There are two major subgenres within Isekai: Reincarnation into another world" and "Transition into another world." However, we at Japan Anime News believe that there’s a third genre worth mentioning when discussing Isekai: "Reverse Isekai." Let’s briefly summarize these three genres.

Reincarnation into another world (Isekai Tensei)
Isekai Reincarnation involves characters who are reborn in another world with memories of their past lives. Notable examples include Mushoku Tensei: Jobless Reincarnation and That Time I Got Reincarnated as a Slime.

Transition into another world (Isekai Teni)
Isekai Transition features characters who move from the real world to another world by some means. Re- Starting Life in Another World and Sword Art Online fall into this category, as do The Twelve Kingdoms and The Familiar of Zero.

Reverse Isekai
Reverse Isekai predates the other two subgenres. It involves characters from a futuristic or fantastical world coming to the present day, like in Doraemon. In Japan, this genre was originally dominant, and Isekai can be seen as a reversal of this concept. For example, Sally, the protagonist of Mitsuteru Yokoyama’s Sally the Witch (1966), comes to the human world from the magical kingdom incognito. Similarly, Rumiko Takahashi’s Urusei Yatsura (1978) features visitors from space using a similar approach. By the late 1980s, harem and romance elements became prominent, giving rise to works like Kosuke Fujishima’s Oh My Goddess!.

These examples demonstrate that the concept of characters from other worlds playing active roles in the modern world has long been a staple of Japanese anime. While not strictly "Isekai," many works feature time travel to the past or future. The topic of time leaps is significant enough to warrant its own discussion, which we will explore at another time.

Isekai and Its Fusion with Other Genres

Robots × Isekai
By the 1980s, many renowned animators were emerging in Japan, enriching content across genres. One key work that cannot be overlooked in discussing Isekai Transition is Aura Battler Dunbine (1983), directed by Yoshiyuki Tomino of the Gundam series fame. In this story, several humans, including the protagonist Sho Zama, are summoned to Byston Well, where they get embroiled in a war involving Aura Battlers, which are essentially robots. On Earth, those who were transported to Byston Well are regarded as having mysteriously vanished.

This story broke new ground by shifting the battleground from the other world back to Earth in the second half. However, at the time, the fantasy genre didn’t have a strong foundation among anime fans, and the complex, mature content typical of Tomino’s works likely prevented it from becoming a major hit. It was later rediscovered as a masterpiece when it was featured in the game Super Robot Wars EX (1994).

Speaking of Super Robot Wars, the second installment, Super Robot Wars 2 (1991), introduced Cybuster, another title with Isekai Transition elements. It seems that Dunbine couldn’t be used due to licensing issues, so an original title with a similar setting was created. The world of La Gias, where Cybuster takes place, was heavily influenced by Dunbine.

Just before the 90s, the robot anime Mashin Hero Wataru (1988) was born. This work was designed as a fun project for children, counterbalancing the serious anime that had been on the rise. It inspired many boys to fantasize about becoming cool heroes in another world.

In shoujo manga, Magic Knight Rayearth (1993) by CLAMP became a massive hit, familiarizing girls with the robot × Isekai genre. The romantic elements with inhabitants of the other world are typical of shoujo manga. In fact, many shoujo manga feature Isekai Transition or Reincarnation settings.

Shoujo Manga and Isekai
Tracing the roots of Isekai in shoujo manga, one of the earliest works is Crest of the Royal Family (1976) (which is still ongoing).The story follows Carol, a girl studying archaeology in the modern world, who gets transported back to ancient Egypt. Her beauty and knowledge of archaeology from the modern era earn her reverence, and she eventually falls in love with King Memphis, though they face numerous challenges. This might be the first work to incorporate romance into an Isekai setting.

In the 1980s, Please Save My Earth (1986) was released. The story follows seven boys and girls who, living in the modern world, gradually remember that they were aliens in their past lives, unraveling mysteries along the way. The story brilliantly intertwined contemporary love with past-life romances, resonating with the trend of trendy dramas in Japan at the time, and tapping into the fear of apocalypse prevalent due to the Nostradamus prophecies.

By the 1990s, Isekai settings were becoming common in shoujo manga, with titles like Fushigi Yugi (1992) and Red River (1995) being released in quick succession.

Meanwhile, we must not forget that we were also traveling to virtual worlds through video games. The next concept to consider is the transition to game worlds.

VR Games and Isekai
One of the most famous works centered on transitioning to a game world is Sword Art Online (SAO). While SAO's impact is undeniable, it’s important to highlight a work that likely influenced it: Bandai Namco Entertainment’s (then Bandai) ".hack" series, which was a pioneering media mix project.

.hack’s first release was the TV anime .hack//SIGN, which aired from April to September 2002. Reki Kawahara began publishing SAO online under the pen name Fumio Kunori in November 2002, so .hack preceded it chronologically.

.hack is set in a fictional MMORPG called "The World," where users enjoy immersive experiences through a face-mounted display. However, some players find themselves unable to return to reality, having lost consciousness while in the game. A group of players becomes aware of these mysterious occurrences and begins to unravel the secrets hidden within the game.

In the early 2000s, online games like Ultima Online (1997) were primarily enjoyed by hardcore PC gamers, with little mainstream appeal (not least because setting up a suitable internet connection was a challenge). In Japan, Ragnarok Online gained popularity due to its gameplay and visual appeal, significantly influencing character design and world-building in VR game × Isekai works.

These two works laid the groundwork for the JRPG × Isekai combination that’s common today. Moreover, the commercial success of hack as a media mix project and SAO as a light novel expanded the range of ways to market a single title.

JRPGs and Isekai
Many of the Isekai works that gained popularity after 2010 and continue to be popular today draw heavily from JRPG elements. JRPGs, or Japanese Role-Playing Games, are epitomized by Dragon Quest and Final Fantasy. This combination is now the mainstream.

JRPGs are characterized by fantasy settings, character growth, magic, and skill systems. Many Isekai works incorporate these elements, such as protagonists in other worlds having game-like stats and growing stronger through battles with monsters—essentially the essence of JRPGs.

One standout example is That Time I Got Reincarnated as a Slime (2013), which clearly integrates common JRPG elements. The novel idea of reincarnating as the weakest monster, a slime, and making that the title itself, has had a significant impact on the genre.

The exponential increase in JRPG-influenced Isekai works owes much to the "Shōsetsuka ni Narō" platform, where anyone can freely post novels.

"Shōsetsuka ni Narō" as the Birthplace of Isekai

Japan’s otaku culture has long featured "doujinshi," or self-published works that add new twists to existing stories. Though selling such doujinshi is technically illegal under copyright law, it’s a culturally accepted practice, and many creators who grew up on doujinshi have shaped this tolerant atmosphere.

As more aspiring writers sought an outlet for their work, the rise of the internet enabled anyone to publish their stories. This cultural backdrop led to the mass production of Isekai fantasy on "Shōsetsuka ni Narō."

On "Shōsetsuka ni Narō," once a popular work emerged, similar concepts with slightly different themes would be posted, or fanfiction would expand on hit works.

The Familiar of Zero became a popular inspiration for fanfiction, leading to a trend of similar works. As more works from "Shōsetsuka ni Narō" were published as books and adapted into manga and anime, a standard route from web novels to commercialization was established.

Re:Zero, Mushoku Tensei, and That Time I Got Reincarnated as a Slime all began on "Shōsetsuka ni Narō."
By the late 2010s, the Isekai genre had become so prolific that it led to a phenomenon akin to an "Isekai boom," with some light novel readers and anime fans growing weary of the constant reincarnation plots. However, as the number of works grew and attracted more fans, the market accepted them, and there was increasing anticipation for the next innovative combination.

For example, Dragon Ball Side Story: That Time I Got Reincarnated as Yamcha is entirely a parody, and its acceptance by readers and editors alike shows how open-minded the community has become. Unexpected combinations like Isekai Suicide Squad further highlight this trend.

Let’s continue to look forward to new works that will make us think, "No way, is that for real!?"

Supplement: The Popularity of Isekai

As discussed, Japan has a long history of themes involving the coexistence of modern and other worlds, or overcoming the challenges they present. Such themes resonate with people’s desire for escapism and the "Ore TUEEE! (I’m so strong)" fantasy.

Moreover, it’s challenging for amateurs to write complete novels. The familiarity of basic JRPG elements—levels, monsters, magic, jobs—requires no explanation, making it easier for aspiring writers to craft stories where the protagonist excels in another world based on their own knowledge. Readers, too, can enjoy connecting their knowledge to the story.

Isekai Anime and Novel Works

Finally, here’s a list of some works mentioned so far. We’ll be creating detailed introduction pages for each, so please stay tuned. Of course, this is just a selection, and there are many more works out there. We ask for your understanding in our curation.

・Aura Battler Dunbine
・The Twelve Kingdoms
・Mashin Hero Wataru
・.hack
・Sword Art Online
・That Time I Got Reincarnated as a Slime
・Mushoku Tensei: Jobless Reincarnation
・Isekai Suicide Squad