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.
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.
Often, Eric is portrayed as a brave and curious character. He's not afraid to explore the unknown, which is how he ended up encountering Ariel in the first place. His love for the sea and his adventurous spirit make him an interesting figure in fanfiction.
One possible fanfiction could be that Ariel and Eric discover a hidden underwater kingdom that was lost long ago. They embark on a journey to learn about its history and find that it holds the key to a magical power that can save both the underwater and land worlds from a new threat.
Perhaps in a fanfiction, Ariel and Eric will have a family of their own. They will raise their children to understand both the land and the sea, creating a unique bond between the two worlds.
One idea could be exploring what would happen if Ariel had a secret power she didn't know about until after she became human. For example, she could have the ability to communicate with all sea creatures, not just the ones she already knew. This would create new challenges and relationships on land.
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.