Light Novel Recommendations: Reverse Isekai

The portal between fantasy worlds works both ways. Not only do characters leap from our primary world to secondary fantasy worlds, characters from those secondary worlds can cross into ours for fish-out-of-water adventures. These fantasies are known by the systematic and admittedly unimaginative label of "reverse isekai" fantasies.

However, the approach between classic isekai portal fantasy and its reverse reflection differs more in just the direction of travel between worlds. Where isekai tends to shove its protagonists through the door between worlds, only to lock the door behind them, reverse isekai stories tend to install a revolving door between worlds. Furthermore, since reverse isekai do not need to rely upon the main character as a stand-in for the reader exploring the world, these stories are far less reliant on wish fulfillment fantasies. This allows reverse isekai stories to offer a wider variety of kinds of stories than the tried and true hero fights against a villain found in traditional isekai portal fantasy.

*****

The Devil is a Part Timer, by Satoshi Wagahara

After the final, climactic battle in another world, the Devil King and his last general are banished to another world: ours. But without magic, they can neither return to their own world, or conquer ours. Forced to make ends meet, the Devil King survives as a lowly fast food employee, with designs of working his way to the top of the company, and then the top of the world. But they aren't the only otherworlders in Japan. The Hero has arrived as well, and she knows where the Devil King works.

A bit of a guilty pleasure, The Devil is a Part Timer combines reverse isekai with the devil/monster genre. Here, Maou is treated more as a demi-human than a proper devil, and the burdens of making ends meet in a low-paying job actually humanize him to the point that he's no longer the same power-mad end boss he once was, much to the consternation and confusion of the Hero, Emilia. The unresolved tension between Maou and Emilia fuels much of the comedy. It is refreshing to see an adult cast evenly divided between the sexes, with actual male friendships that aren't handwaved off screen in favor of harem hijinks or romanticized for fetishes.  The worldbuilding leans heavily on Kabbalah, which some might find off-putting, but becomes important when the powers that be in the old world won't leave Maou and Emilia alone in ours. The Devil is a Part Timer is a humorous refuge from wish-fulfillment and harem fantasies that still brings sword and magic action to the table.

*****

Notable mentions for straight isekai portal fantasies include: Re: Zero--Starting Life in Another World, by Tappei Nagatsuki, where a teen from our world finds himself in a new world with the mysterious power to reverse time by dying--a lot, and the recently released Mushoku Tensei, by "Rifujin na Magonote," where an unsuccessful man in his thirties resolves to do better in his new life, even if it means challenging a god.

Reverse isekai notable mentions include Outbreak Company, by Ichiro Sasaki, in which a fandom-obsessed teen is tapped by the Japanese government to export fandom to another world, and Restaurant in Another World, by Junpei Inuzaka, which combines cooking stories and slice-of-life stories as it follows the stories of adventurers from other worlds that have found their way to a restaurant in ours.