I think Misty from the Pokemon world could be a main character in this fanfiction. Since she has a connection with water - type Pokemon, she could easily fit into the underwater world of The Little Mermaid. Along with her, a Psyduck would be there. Psyduck's clumsy yet powerful abilities could add an interesting element to the story. And of course, Ariel would be a main character. She could learn a lot from Misty about the Pokemon world and they could team up to protect both their worlds from any threats.
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.
Obviously, Ariel would be one of the main characters. She'd be the mermaid trying to navigate high school life. Eric could also be there as the love interest. Maybe Flounder could be her sidekick, a fish - out - of - water (literally) in the high school, always getting into comical situations. And Ursula could be the school bully or the antagonist who tries to make Ariel's life miserable.
A sea - faring cat could be a new character. This cat has a special bond with the sailors on Prince Eric's ship. When Ariel comes on board, the cat is immediately suspicious of her. But as time goes on, they form an unlikely friendship, and the cat helps Ariel understand some of the human ways that the sailors have.
Maybe a lost princess from a sunken city. She has been in hiding for a long time because of some danger that destroyed her city. She meets the little mermaid and they become friends. The lost princess has unique powers related to the ancient magic of her sunken city, and she shares these powers with the little mermaid to help her in her quests.
Obviously, the Little Mermaid herself would be a main character. She could be joined by her friends from the sea, like a talkative seahorse or a wise old octopus who gives her advice from afar. At Ever After High, her roommates or classmates like Apple White or Raven Queen could also be important characters. They could help her adjust to school life on land.
Obviously, Lily is one of the main characters. She's the mermaid around which the story revolves.
One possible plot could be that a Pokemon, like Vaporeon which has a mermaid - like appearance, gets transported to the world of The Little Mermaid. It befriends Ariel and helps her in her quest to understand the human world. Vaporeon could use its water - based powers to protect Ariel from Ursula's evil plans.
The plot might start with Serena finding a strange, enchanted shell on the beach. When she touches it, she is turned into a mermaid. In this new form, she realizes she can communicate with water - type Pokemon in a different way. She embarks on a journey to find the origin of the shell and the power that transformed her. Along the journey, she makes new friends among the mermaids and Pokemon, and together they face a powerful villain who wants to use the shell's power to take over both the sea and the land.
In a 'little mermaid lemon fanfic', one of the main characters would be the little mermaid. She would be the central figure around which the story revolves. Another main character could be an old sea witch who has a connection to the lemon - related magic in the ocean. Maybe she gives the mermaid a task involving lemons in exchange for something. And a third main character could be a young human prince who loves all things lemon - flavored and is drawn to the mermaid because of her unique lemon - like charm.
For a 'Little Mermaid Naruto fanfic', Naruto and Ariel are the primary ones. However, Gaara could be an interesting addition. His past of being an outcast could parallel Ariel's feeling of not fully belonging in her own world sometimes. Then we have Ursula, the sea witch from the Little Mermaid story. In this fanfic, she could be a powerful enemy who wants to use Naruto's chakra for her own evil purposes. And Hinata could be another character, her shy nature contrasting with Ariel's more adventurous spirit as they both interact with Naruto in this unique crossover.