A great plot for little merman fanfiction could be that he has a unique ability to communicate with all sea animals, including the most dangerous ones. His ability is needed when a large sea monster starts attacking ships and the underwater kingdoms. He has to use his power to understand the monster's motives and find a way to stop it, all while dealing with the politics and rivalries within his own merman society.
One idea could be that the little merman discovers a hidden underwater kingdom full of magic and mystery. He could be on a quest to find a powerful artifact that can save his own kingdom from a dark force. Another plot could be a love story where he falls in love with a human who can also breathe underwater due to a special spell.
Perhaps the little merman gets lost in a storm and washes up on a strange shore. There, he meets a group of friendly sea creatures that are different from those in his home. They help him on his journey back home, and along the way, he learns about different cultures and ways of life in the ocean. He could also face some villains who are trying to stop him from getting back.
One idea could be to explore what would happen if the Little Mermaid had a different power, like the ability to control storms. Another could be a story where she meets a merman from a different part of the ocean who has a completely different culture. Maybe a fanfiction where she has to save the entire ocean from a new kind of threat that no one has ever seen before.
Maybe Harry is the only merman in a world where mermaids are common. He faces discrimination at first but then uses his unique abilities to save the underwater kingdom from a great danger. For example, he might have a special power to purify poisoned waters that the mermaids don't have.
Well, a cool plot might be that there's a merman who has a special power to control water currents, and Percy needs his help to find a lost magical artifact deep in the ocean. In return, Percy has to help the merman get accepted by the surface - dwelling gods. Or perhaps a merman is wrongly accused of stealing Poseidon's trident and Percy has to prove his innocence.
A plot could be that Eric, as a merman, is part of a group of mermen who are at war with a different underwater species. Ariel gets caught in the middle of this conflict. Eric has to choose between his loyalty to his kind and his growing feelings for Ariel. This would create a lot of drama and tension in the fanfiction.
One idea could be exploring Ariel's life after she becomes human. Maybe she has trouble adjusting to some of the more mundane aspects of human life, like cooking or doing laundry. Another could be a story where Ursula's sister comes to seek revenge, but Ariel has to convince her that not all humans are bad.
One idea could be exploring the relationship between Melody and a new mermaid friend from a different part of the ocean. They could go on adventures together and discover hidden treasures.
One idea could be exploring an alternate ending where Jo actually marries Laurie. It would change the whole dynamic of the story and show a different side of their relationship.
One idea could be to explore what would happen if Sara Crewe had a secret magical ability that she discovered while in the attic. For example, she could be able to communicate with the mice in a more profound way and they help her find a hidden treasure in the old house.
Another plot could be about the mermaid learning more about the human world in a different way. Instead of just falling in love with the prince, she discovers a hidden talent among humans like music or art and tries to bring it back to the underwater world. This could create a whole new set of adventures and challenges for her. For example, she might have to find a way to communicate with a human artist without revealing her true identity at first.
Maybe in the little Avengers fanfiction, they go on a quest to find a special artifact that can only be accessed by those of small stature. Along the way, they face challenges like tiny traps and miniature monsters. Each of the little Avengers, such as a young Spider - Man, could use their unique abilities to overcome these obstacles. They could also have a mentor, like a shrunken version of Iron Man, guiding them through their adventure.