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.
In this fanfiction, Vanessa might have a change of heart. She realizes that her actions are wrong and decides to help Eric find Ariel. Along the way, they share many adventures and grow closer. Eric begins to see Vanessa as a friend, and she has to suppress her growing feelings for him. Their relationship is filled with tension as Vanessa battles her own emotions while trying to do the right thing.
The relationship could develop in a negative way. Vanessa might start to be more controlling over Eric as she realizes he is starting to have doubts. She could try to use more powerful magic to keep him in line.
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.
One possible plotline could be Vanessa's backstory. Maybe she was once a kind - hearted woman who was corrupted by dark magic. Another could be a redemption arc, where she tries to make amends for her actions against Ariel. For example, she might help Ariel in a difficult situation, like facing a new threat in the ocean world.
One way to develop Vanessa is to make her a more complex villain. Instead of just being a tool of the sea witch, she could have her own plans and desires. Maybe she wants to rule the underwater world herself. This would create more conflict and also give her character more depth. We could also explore her relationship with other characters in the story, such as the prince's family or the servants in the palace.
Ursula as a mermaid in fanfiction might also explore her backstory more deeply. She could have been a mermaid princess in a far - off part of the ocean. But due to a power struggle or a curse, she lost her status and became the villain we know. This could add a lot of depth to her character and make the fanfiction really engaging.
Prince Eric could be a main character. He would be important as he is Ariel's love interest. Also, King Triton, Ariel's father, could play a significant role as he would be concerned about Ursula's return and want to protect his daughter and the kingdom.
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.