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 possible story could be that Eric, as a merman, is an outcast in his own underwater kingdom. Maybe he has different ideas about interacting with the surface world compared to the other mermen. He could befriend Ariel, who is curious about his unique perspective among the mermen.
Perhaps in the fanfiction, Ariel and Eric get married and have to deal with the cultural differences between the underwater world and the human world. For example, Ariel has to learn the proper etiquette in Eric's kingdom while Eric tries to understand the unique traditions of Ariel's mermaid family.
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.
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.
In the fanfiction, a romantic plot could involve Ariel getting the ability to walk on land permanently. Eric then takes her on a tour of his kingdom, showing her all the beautiful places. At sunset, he takes her to a cliff overlooking the ocean and proposes to her, making it a very romantic scene.
One possible plot could be that Eric, after being under Vanessa's spell briefly, has hazy memories of Ariel. Vanessa tries to keep Eric away from the sea, but Eric starts having dreams of a mermaid. As he investigates, he discovers Vanessa's true nature. He then sets out to find the real girl he saw in his dreams, leading him back to Ariel.
Well, a plot idea might be that Melody is kidnapped by a group of mermaids from a far - off ocean. These mermaids think Melody has special powers that can help them save their dying reef. So, Melody has to figure out a way to either convince them she doesn't or actually find a way to help them. Also, perhaps Melody finds a magical object that gives her the ability to talk to sea animals in a different way, like she can understand their ancient languages. This could lead her on a quest to find the origin of this magic and how it can be used for good in the ocean world. Another one could be that Melody is cursed by an evil sea witch who wants to take over Atlantica through her. Melody has to break the curse while also protecting her family and kingdom.
One idea could be that Athena, as a mermaid, discovers a hidden underwater kingdom that has been forgotten by time. She could then embark on a journey to learn about its history and secrets.
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.