One interesting concept could be a universe where the Ice King is a benevolent ruler instead of a somewhat antagonist figure. He could use his ice powers for good, like creating beautiful ice sculptures all over the Land of Ooo to beautify it.
In some fanfictions, there might be an alternate universe where Finn and Jake have different origins. For example, Finn could be from a family of powerful magic users rather than being a human raised by dogs. This would completely change his relationship with magic in the story and how he approaches various adventures.
Another concept could be an alternate Ooo where the Candy Kingdom is a totalitarian state. Princess Bubblegum, instead of being a mostly benevolent leader, has become extremely controlling. This would lead to a whole new set of adventures for Finn and Jake as they try to either reform the kingdom or deal with its consequences for the rest of Ooo.
In RWBY alternate universe fanfiction, a cool idea is that the characters switch roles. Yang could be the shy, bookish type while Weiss is the brash, party - loving one. Also, the Dust element could be completely different. Instead of being a resource mined from the earth, it could be something that is created through magic. Additionally, an interesting concept is an AU where the characters are in a modern, non - combat setting, like a high school drama where they still have their unique personalities but deal with normal teenage problems.
One interesting concept could be a Naruto AU where the ninja world is a modern, high - tech society. Instead of using traditional ninja tools, they use advanced weapons and gadgets. Another could be an AU where the main characters have different elemental affinities than in the original story, which would change their combat styles and relationships.
Some fanfictions in the Avengers alternate universe explore the idea of the Avengers being part of a post - apocalyptic world. In this setting, they might have to fight against new and more dangerous threats that emerged from the ruins. Maybe there are mutated creatures or a new breed of supervillains. Also, an alternate universe could feature a younger version of the Avengers, like teen versions, and their journey of growing into heroes while dealing with the typical teenage problems along with the super - hero stuff.
One interesting concept could be if the characters had different careers. For example, instead of being in a glee club, they could be professional dancers in a big city dance troupe. Another concept might be a world where the glee club is a secret society with special powers related to music.
In this type of fanfiction, the concept of character evolution is fascinating. In an alternate universe, the characters may face different challenges that accelerate or change their growth. For instance, Yang might have to overcome a different kind of personal trauma. Also, the concept of the alternate universe's history and how it affects the RWBY characters is interesting. Maybe there was a different Great War in one universe, and that has shaped the current state of the world and the characters' place in it.
A third concept could be a Hunger Games where the Capitol has a different set of values. Instead of valuing brutality and spectacle, they value intelligence and artistry. So the games are more about solving complex puzzles and creating beautiful works of art while still in the arena, and the winner is chosen based on those criteria.
There are often concepts in alternate universe fanfictions where Spider Man is part of a different culture. For example, in a Japanese - inspired universe, he could be a samurai - like hero, with his webs being more like silk cords used in traditional Japanese weaponry. His suit might also be designed with elements of Japanese armor, and his battles could be more about honor and code, rather than just stopping crime.
One interesting concept could be a universe where Tony Stark is a sorcerer instead of a tech genius. He could use magic in ways similar to how he manipulates technology in the main universe. Another concept might be a world where he's a pirate, sailing the high seas with high - tech ships and weapons of his own creation. Also, an alternate universe could have Tony as a teacher, passing on his knowledge of science and innovation to the next generation.
In some Young Justice alternate universe fanfictions, there might be a world where the characters have different powers or abilities. Maybe Aqualad has fire - based powers instead of water - based ones. This can lead to new storylines and character developments as they adapt to these changes.
In Naruko fanfiction, one interesting concept could be a world where Naruko has a different set of ninja skills. For example, she might master a unique form of water jutsu that no one in the original Naruto universe has seen before. Another concept could be her relationships being completely different. Maybe she forms a strong bond with characters who were antagonists in the original story, like Orochimaru, but in this alternate universe, he has a different, more positive role to play. Also, the idea of Naruko leading a different ninja team with members from different villages could make for an exciting plot.