A young African girl could be a main character. She might take Naruto under her wing, showing him around the village and teaching him about African traditions like dancing and making handicrafts. Also, a powerful African sorcerer could be in the story. He might view Naruto as an intruder at first but then realizes Naruto's good intentions and teams up with him to fight against a common enemy that threatens both their worlds.
There could be an African hunter as a main character. He could be impressed by Naruto's speed and stealth, which are similar to his own hunting skills. The hunter could teach Naruto about tracking animals in the African wilderness. And perhaps a storyteller in the African village would also be important. He would be the one to spread Naruto's tales throughout the village and beyond, adding to Naruto's growing legend in Africa.
Maybe Naruto is sent to Africa on a mission by the Hidden Leaf Village. Once there, he discovers a new world full of different cultures and challenges. He could encounter magical creatures or powers that are unique to Africa in this fanfic. And he has to use his wits and ninja powers to either protect these newfound elements or to stop an evil force that is threatening both Africa and his own village back in Naruto's world.
He could meet a local superhero. They might initially clash because they have different ways of doing things, but then they realize they can learn from each other. For example, Naruto could teach the superhero about chakra control and the superhero could teach Naruto about modern technology and fighting strategies used in America.
Hinata could be an idol trainee. She is shy at first but as she trains, she becomes more confident. Naruto could be her biggest supporter, and their relationship could develop further as they both pursue their dreams in the idol and ninja worlds respectively.
There could be members of the Gremory family. For example, Rias Gremory might be a key character. She could be one of those who initially neglect Naruto but later come to realize his potential. Another character could be Issei Hyodo, who might be in a position where he has to choose between the traditional Gremory way and Naruto's different approach.
There's also a chance that a new, unknown character could be the main antagonist. This character could be from a far - off land with a vendetta against the Hidden Leaf. They target Naruto specifically and use some ancient and evil method to drive him crazy. Since Naruto is so important to the Leaf, this would create a lot of chaos and make the new character the main source of trouble for Naruto and the village.
One possible plot is that Naruto arrives in America and is initially confused by the different culture. But then he starts to adapt. He could use his chakra to perform amazing feats at a local circus or fair, becoming a local sensation. He might also encounter some villains who are after his ninja powers and he has to fight them off while trying to keep his identity a secret.
There could be a new character introduced, perhaps an old hermit who is an expert in sealing. This character could have some hidden motives, like using Naruto's newfound skills for his own gain at first but then eventually becoming a true ally after seeing Naruto's pure intentions with the power of sealing.
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.
Sakura could be a main character. She is a skilled medic - ninja. So, she might be involved in trying to figure out why the flowers are wilting. Maybe she thinks it's related to some new disease in the plant life of the Naruto world and she uses her medical knowledge to investigate.
Sakura could be a great main character. You could show her growth during the bell test, not just as a ninja in terms of skills, but also in her self - confidence. Maybe she has to take the lead when Naruto and Sasuke are incapacitated for some reason.