Adventure is a very common theme. Since 'One Piece' is all about the grand adventures of the Straw Hat crew, fan fictions often continue this trend, taking the characters on new and exciting journeys. Another common theme is friendship. Just like in the original, characters in fan fictions rely on their friendships to overcome difficulties.
One popular 'One Piece' fan fiction is 'The Pirate's Daughter'. It offers an interesting take on the world of 'One Piece' with a new character, a daughter of a famous pirate, who embarks on her own adventure. Another one could be 'New Alliances' which focuses on unexpected alliances between different pirate crews in the 'One Piece' universe.
First, you should have a good understanding of the One Piece world, including its characters, their abilities, and the overall story arc. Then, think of an interesting concept, like a new adventure for the Straw Hats or a different take on an existing event. After that, start writing a simple outline of your story, with a beginning, middle, and end.
If Law is hurt in a fan fiction, it can change the power dynamics in the story. For example, if he's injured before a big battle against a common enemy, his crew might have to step up more. It can also create new alliances as other characters come to his aid.
One popular theme is the backstories of minor characters. Writers often explore what led them to become pirates or join certain crews. Another theme is alternate universes, like if Luffy had a different devil fruit power. And of course, there are many fan fictions about the relationships between the characters, whether it's friendship or something more romantic.
One way to start is by looking at the most popular fan fiction websites. Websites like Archive of Our Own (AO3) have sorting and filtering options. You can try sorting by word count in descending order to see some of the longer ones. However, this may not be a foolproof method as there could be some very long fan fictions on other less - known platforms.
The Straw Hat shinobi could be a new character who combines the characteristics of both Naruto - style shinobi and One Piece pirates. He might wear a straw hat like Luffy and have ninja abilities.
Well, it could be about a shinobi who somehow gets involved with the Straw Hat crew in a world where Naruto and One Piece universes collide. Maybe the shinobi has some special abilities that are useful to the crew on their adventures.
One common theme is Nami's growth as a character. Fan fictions often explore how she becomes stronger, both physically and mentally. Another theme is her relationship with the other Straw Hat crew members, like her sisterly bond with Robin or her banter with Luffy.
One popular 'One Piece fan fiction' is the one where Luffy has a different power-up. It's interesting as it shows a new side of his strength. Another is about the backstories of the minor characters in more detail, like Buggy the Clown's early days. And there's also a fan fic that focuses on a time - travel concept, where the Straw Hat crew goes back in time to change certain events in the One Piece world.