Reverse isekai novels are unique because they flip the typical isekai formula. Instead of a character from our world going to a fantasy world, it's the other way around. This creates interesting scenarios where characters from magical or otherworldly places have to adapt to our modern, often mundane world. For example, in 'The Devil is a Part - Timer!', the Devil King has to deal with getting a job at a fast - food joint in Tokyo.
One popular reverse isekai novel is 'KonoSuba: God's Blessing on this Wonderful World!'. In this story, characters from a fantasy world end up in the real world, creating all sorts of comical and chaotic situations. Another is 'The Devil is a Part - Timer!', where the Devil King and his minions are forced to live in modern - day Tokyo and have to adapt to normal human life, like getting part - time jobs. There's also 'How Not to Summon a Demon Lord', which has elements of reverse isekai as the demon lord gets summoned to our world in an unexpected way.
The main thing that makes'reverse isekai light novels' unique is the role reversal. Instead of the typical isekai where a character from our world goes to a fantasy world, in reverse isekai, it's often a character from a fantasy world coming to our world. This leads to a lot of comical and interesting situations as they have to adapt to modern technology, social norms, etc.
There's also 'I'm Standing on a Million Lives'. The main character is a gamer who gets dragged into a parallel world. This is a reverse isekai in that the character from our world has to adapt to a different, more dangerous world filled with challenges and quests, and the story unfolds with a lot of interesting twists and turns.
A great'reverse isekai fanfic' example is when a powerful wizard from a medieval - like magical world is transported to our world. He might be baffled by things like cars and electricity at first. Also, there are those where a mermaid somehow ends up in a human city near the coast. She has to deal with walking on legs for the first time and learning about human customs. These kinds of stories often explore how characters from otherworldly settings interact with and adapt to our modern or different world.
Well, in reverse harem isekai web novels, a prevalent theme is the struggle for acceptance. The female character, being from another world or reincarnated, has to strive to be accepted in the new society. Another theme is the exploration of different personalities within the reverse harem. Each male character has a distinct personality, and the female lead has to understand and interact with them. Additionally, the theme of growth, both personal and in terms of power or status, is common. As she faces challenges in the new world, she grows as a person and often rises in power or influence among the male characters in her harem.
To start writing a'reverse isekai fanfic', begin with creating the character from the other realm. Consider their personality, powers, and backstory. For instance, if it's a powerful sorceress, what led her to be in this position? Next, figure out the method of transportation to our world. It could be a portal opened by a mad scientist in our world by accident. Then, when they arrive, describe their shock and confusion. Maybe they see a cell phone and think it's some sort of magic device. You can then build the story around their attempts to adapt and the relationships they form in this new world.
For me, 'That Time I Got Reincarnated as a Slime' stands out. The world-building and plot development are really engaging. Also, the characters have a lot of depth.
Well, it's a bit hard to pinpoint exactly which was the very first one. But some early examples could include 'El-Hazard: The Magnificent World', which had elements of the isekai genre.
Isekai Quartet indeed has a manga. It offers a different perspective and sometimes delves deeper into the story compared to the anime. The manga can be a great companion to the animated version for fans wanting more of the Isekai Quartet world.