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.
Eric as a merman could have a backstory where he was once a human but was cursed to become a merman. In the fanfiction, he would be on a quest to break the curse. Along the way, he meets Ariel, and they team up. Ariel helps him understand the underwater world better, while he shares his knowledge of the human world with her. Their friendship could gradually turn into something more as they face numerous adventures together.
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.
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.
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.
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.
Well, one idea for this fanfiction could be that Vanessa, in her quest to keep Eric away from Ariel, tries to make him believe that mermaids are evil. She weaves tales of sea monsters and how mermaids are their allies. However, Eric has his doubts. He has seen Ariel's pure heart and can't quite believe Vanessa's stories. As he starts to investigate, he uncovers Vanessa's true identity and her devious plans.
One possibility is that they immediately start planning their future. Since they come from two different worlds, they'd have to figure out how to make their relationship work. Maybe they start building a place where both of them can be comfortable, half on land and half in the sea. And they could start spreading the message of love and unity between humans and mer - people.
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 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.
A great storyline could involve Eric's adventures before he met Ariel. Maybe he was on a quest to find a mysterious island, and during that journey, he had some premonitions or signs that led him to Ariel later. It could also be about Eric dealing with the political pressure in his kingdom regarding his marriage to Ariel, as she is from a different species.