Since we should avoid adult content, instead we can talk about some general alternate universe stories. For example, in some alternate universe stories, characters might have different powers or live in a world with different social structures. 'A Wrinkle in Time' by Madeleine L'Engle has elements of alternate universes where the characters travel through different dimensions.
Definitely check out 'Age of Apocalypse'. It's an alternate reality where Apocalypse rules. The X - Men are in a fight for survival against his tyranny. It has a great mix of action and character development. You get to see characters like Magneto taking on different roles as they struggle to oppose Apocalypse's regime.
One characteristic is the existence of different rules. For example, in some alternate universe fictions, the laws of physics may be different. Another is the different social structures. There could be a world where monarchy still reigns supreme. Also, unique creatures often appear, like in 'His Dark Materials' where there are daemons.
Well, in the world of 'alternate universe fanfic', for shows like 'Doctor Who', there could be an AU where the Doctor is a human instead of a Time Lord. In 'Sherlock' AUs, Sherlock and Watson might be in a steampunk universe. And for 'The Hunger Games', an AU could be that there is no Hunger Games at all and the districts live in a utopian society.
The 'Marvel Zombies' storyline is another interesting alternate universe story. In this, many of the Marvel heroes are turned into zombies. It's a unique take on the superhero genre as it combines horror elements with the familiar superheroes. It shows how even the mightiest heroes can be vulnerable in a different set of circumstances and how the world would react to such a terrifying transformation.
One great 'alternate universe naruto fanfiction' is 'Road to Ninja: Naruto the Movie - Another Side'. It presents a very different Naruto world where characters have different personalities and roles. For example, Naruto has a family in this AU which changes his whole dynamic.
There's also 'Batman in a Cyberpunk Alternate Universe'. This fanfic takes Batman into a high - tech, dystopian future. Bruce Wayne uses advanced cybernetic enhancements and battles against tech - savvy villains in a neon - lit Gotham filled with skyscrapers and flying cars.
Perhaps he meets a version of his parents who are still alive. This would be an incredibly emotional encounter for Harry. He would get to know them, and they could teach him things about magic and life that he never had the chance to learn before.
One idea could be a castle that floats in the sky in the alternate universe. It could be made of some kind of magical crystal that gives it the ability to levitate. The inhabitants of this castle might be a race of winged beings who use the castle as a base to protect their realm from dark forces.
I really like 'Time - Twisted Love' in the 'Harry and Ginny alternate universe fanfiction' genre. It plays with time travel and shows Harry and Ginny meeting at different points in time in a really convoluted but fascinating way. 'The Magic Within' is another one where Ginny discovers a new type of magic that only she can use, and it changes the dynamic between her and Harry. Also, 'Hidden Worlds' is a great read. It's about Harry and Ginny finding a secret world within Hogwarts that no one else knows about and how that impacts their relationship.