Isekai is an expansive anime genre that's spawned several subgenres and tropes, with many series essentially being "isekai, but with X variation." One of these tropes is the "betrayal isekai," where the main characters are suddenly turned on by friends, allies or society as a whole. Examples of these range from light novels to manga and anime, all of which put their heroes through the ringer.
Betrayed isekai protagonists fight against disloyalty from all sides in their reincarnated world. The stories also play on the supposed "power fantasy" nature of the genre, putting their heroes at the bottom of the societal rung to see them climb up by some grueling actions. Here's a look at some great examples of this trope and where to read and watch them.
Her Majesty's Swarm
Her Majesty's Swarm is a rather interesting take on the "bug reincarnation" trope of isekai, as well as the revenge trope. The story involves a college student who's a huge fan of an online game where she plays in the evil faction known as Arachnea. Like many isekai protagonists, she suddenly finds herself reborn into the world of the game, now in the body of a young teenage girl who rules the Arachnea faction.
She quickly becomes accustomed to being worshiped by her insectoid swarm, but this cruel new universe has several tricks to play. The protagonist soon loses one of her swarm, with nearby villagers also massacred for no reason. Now bent on gaining revenge on a world she once loved so much, she uses her knowledge of the "game" to enact vengeance.
Her Majesty's Swarm is created by the interestingly named author 616th Special Information Battalion, with Eiri Iwamoto illustrating the light novels. There has also been a manga adaptation, and with the novels localized and available in English through retailers like Amazon, its growing popularity could see it get an anime adaptation.
Tsukimichi: Moonlit Fantasy
Created by Kei Azumi and Mitsuaki Matsumoto, Tsukimichi: Moonlit Fantasy is very much a reverse power fantasy. The hero, Makoto Misumi, is reincarnated into a fantasy world to serve as its hero. Unfortunately for him, the goddess behind this idea quickly abandons him and the pact she'd made with his parents beforehand due to Makoto not being deemed beautiful enough in her eyes.
He's then cast aside by society as a whole, with his new world wanting nothing to do with him. Ironically, Makoto also develops several incredible powers which allow him to begin changing the world for the better. Tsukimichi started in 2012 as a web novel before becoming a light novel series, a manga and finally an anime. The latter is the only localized entry in the franchise currently, and it can be streamed through Crunchyroll.
Arifureta: From Commonplace to World's Strongest
Arifureta protagonist Hajime Nagumo has a pretty tough life. In his normal life on Earth, he's bullied and made fun of by his classmates. Upon being transported to another world with them, things don't really improve. Hajime is given the most rudimentary of magical abilities, paling in comparison to his classmates' impressive new powers. On a mission to take down monsters in a dungeon, one classmate finally betrays him and knocks him off of a bridge, seemingly to his death.
Hajime survives, however, and hones many powerful abilities and weapons upon escaping certain doom. He's soon joined by other outcasts who make up his party as he strives to survive this cruel new world. Like other isekai, Arifureta also transitioned from novel to manga to anime. The manga and light novels can both be purchased through Amazon and other retailers, while the anime can be streamed on Funimation and Hulu.
The Rising of the Shield Hero
One of the more controversial examples of a "revenge" or "betrayal" isekai is the now-infamous The Rising of the Shield Hero. Protagonist Naofumi is one of several to be reincarnated into a new fantasy world. He was given a shield as a weapon, making him defensive and reactive in combat while the others received more offensive weapons. To make this seemingly bad luck even worse, Naofumi is soon turned on by the entire kingdom when his companion, the princess, leaves him derelict and accuses him of assaulting her.
Now firmly on his own and forced to survive to fend for himself, Naofumi finds aid in a bird monster and a tanuki girl. Together, they try to commit heroic acts for a world that scorns and hates Naofumi, with his betrayal threatening to keep him from unraveling an important mystery. The aforementioned use of a false rape accusation caused quite the scandal in the West, but nevertheless, Shield Hero has become quite popular.
The light novels and manga can be bought from Amazon, Barnes and Noble and other retailers, as well as listened to on audiobook programs such as Audible. Meanwhile, the Shield Hero anime can be streamed on Funimation and Crunchyroll, with Prime Video offering individual episodes for purchase.