Maybe Kakashi. Kakashi is very experienced and wise. He could offer Naruto valuable advice on leading the crew and dealing with the various situations they might encounter at sea. Also, his Sharingan could come in handy in detecting hidden threats.
It could be Shikamaru. Shikamaru is smart and good at strategizing. He would be able to plan the ship's routes and come up with plans to outwit their enemies. His lazy - but - efficient attitude would also add an interesting dynamic to the crew.
Sasuke could be his first mate. Despite their past differences, Sasuke's skills as a ninja would be useful on the ship. He could be in charge of security and combat strategies.
The plot could involve Naruto using his ninja skills on the high seas. He might use his shadow clone jutsu to man different parts of the ship during battles. For example, one clone could be at the helm, steering the Black Pearl away from danger while the real Naruto is fighting off pirates using his Rasengan.
The plot could involve Naruto assembling a unique crew. He'd pick people not just for their sailing skills but also for their hearts. With Naruto as captain, the Black Pearl could travel to mysterious islands, like those filled with ancient ninja artifacts lost at sea. His leadership would be tested when facing powerful pirate lords who want to take over the Black Pearl and use it for evil deeds.
It could be Hermione. In some alternate interpretations, there could be a situation where Hermione, while trying out a new and powerful magic, accidentally hurts Harry. Their friendship is put to the test as Harry has to deal with the pain and Hermione has to come to terms with what she's done.
Maybe it's Ron. Suppose Ron gets jealous of Harry's fame and power and, in a moment of weakness and envy, decides to abandon Harry to die. This would create a lot of drama as Ron and Harry have been friends for a long time, and such a betrayal would be a huge shock to the story's readers.
The main characters are, as the title suggests, the captain and the first mate. They are the key figures in any story related to a ship's operations and crew management. The captain is in charge of the whole ship, making major decisions, while the first mate is his right - hand man, helping with various tasks and taking over when the captain is unavailable.
In the fanfiction, the black pearl might be a symbol of something important. It could represent a long - lost hope for a certain clan or village. Naruto, with his kind heart and strong will, might be the only one who can unlock the true potential of the black pearl. Maybe it contains the memories or powers of an ancient sage, and Naruto has to learn how to access them to save his friends or the entire ninja world.
The Black Pearl could be a treasure in the One Piece world that somehow ends up in the Naruto world. This could cause chaos as the shinobi are not used to such a valuable and strange object. Pirates from One Piece might then travel to the Naruto world to retrieve it, leading to all sorts of interesting interactions between the two groups.
One possible fanfiction could be about a crossover where characters from Naruto and One Piece encounter a mysterious Black Pearl. Maybe the pirates from One Piece are searching for this powerful pearl which has some sort of chakra - like energy. And the ninjas from Naruto are also interested because it could enhance their jutsu. They end up in a battle for the pearl, but then realize they can work together to understand its true power.
Naruto's determination would be a great fit. He never gives up in the ninja world, and as captain, he'd be the same on the high seas. For example, if the Black Pearl was caught in a storm or facing a powerful enemy, he'd keep pushing forward. His loyalty would also extend to his crew. He'd protect them at all costs, just like he does with his friends in the ninja world.
It could be the Death Eaters. Even if they are on the 'bad side', they might see an opportunity to disrupt Harry's life and weaken him. By forcing him to reject his mate, they can create emotional turmoil for Harry, which would make him less focused on fighting against them.