The main characters could be a dashing pirate captain, like Captain Jack Sparrow - style, full of charm and a bit of roguishness. And a beautiful mermaid with long flowing hair and a kind heart. The contrast between his rough and tumble world and her serene underwater existence would create great tension and chemistry.
For the Pirate Isles side, a swashbuckling pirate captain like Captain Blackbeard could be a main character. He could bring his tough and adventurous spirit into the Mystreet world. On the Mystreet side, Aaron could be a main character. His strength and loyalty would be interesting to see when dealing with the pirates.
A mermaid named Nami could be one of the main characters. She might be a curious and adventurous mermaid who is the first to approach Naruto. Another could be Marina, a more reserved mermaid but with great wisdom. She could act as a sort of advisor to Naruto within the mermaid world.
In mermaid x pirate fanfiction, the theme of power dynamics often comes up. The pirate may initially have power over the mermaid as he captures her or has some advantage in their first encounter. But as the story unfolds, the mermaid's unique abilities can turn the tables. There's also the theme of loyalty. The pirate has loyalty to his crew, but his feelings for the mermaid can put that loyalty to the test. And finally, the theme of mystery. The mermaid's world and her abilities are often mysterious to the pirate, and this mystery drives the plot forward as he tries to understand more about her.
Phoenix Wright could be one of the main characters. He could be drawn into a case involving pirates, using his sharp legal mind to defend them or prosecute them depending on the situation. Another option could be Apollo Justice. His ability to perceive lies could be really useful in a pirate - themed courtroom drama, especially when dealing with untrustworthy pirates. And of course, Maya Fey could also be involved, perhaps using her spirit - channeling abilities to uncover hidden truths related to pirate crimes.
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.
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.
There could be a friend of Bella's, like a human friend who starts to suspect that something is different about Bella. This character could add an interesting dynamic as they try to figure out Bella's secret and support her at the same time.
One idea could be a pirate captain who discovers a mermaid in his ship's hold. She was captured by his crew thinking she was a good luck charm. The pirate, against his tough exterior, starts to feel sympathy for her and tries to protect her from his more superstitious and cruel crew members.
One popular mermaid x pirate fanfiction is 'The Mermaid's Pirate Captor'. It tells a story of a mermaid who is captured by a pirate and how their relationship evolves over time. There's also 'Pirate and the Mermaid's Quest' which involves the two characters going on an adventure together.
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.