Well, the plot could involve the original character (oc) suddenly finding themselves in Luffy's world. Maybe they are reborn as a new member of the Straw Hat crew. They could have unique abilities from their previous life that help the crew in their adventures, like being able to sense danger more acutely or having a special knowledge of some hidden treasures.
It could be a new character created specifically for the fanfiction. Maybe a powerful pirate who has a vendetta against the Straw Hat crew because of the oc's presence. Since the oc is reborn into this world, they might bring some sort of change that angers this new antagonist.
The theme of acceptance is quite common. Fem Luffy often has to be accepted by the other characters in the story. This could be because she's different due to her gender or her slightly different personality traits. Also, the theme of self - discovery is prevalent. As fem Luffy navigates the pirate world, she discovers more about herself, her abilities, and her place in the grand scheme of things.
A possible fanfiction could be about blind Luffy being mistaken for a powerful shinobi because of his strange abilities. His rubbery body and unique way of fighting, combined with his enhanced non - visual senses, could make the Naruto characters view him as a mysterious and dangerous opponent or ally. This could lead to all sorts of adventures and misunderstandings as he tries to navigate the complex world of ninjas.
However, in the world of One Piece, it's been said that eating two devil fruits would cause a person to explode. But in fanfiction, this rule might be bent. Another consequence could be that Luffy's personality changes. The new devil fruit power might come with some sort of consciousness or influence that alters his decision - making or how he views the world. He might become more aggressive or more cautious depending on the nature of the new power.
Well, Luffy in the Naruto world would be an interesting mix. His carefree nature might clash with the more serious and disciplined ninja lifestyle. However, his ability to stretch and his powerful attacks could make him a formidable ally. Maybe he'd team up with the Akatsuki by accident, thinking they were just a group of misfits like his own crew, but then realize their true nature and fight against them.
They could start with a big hug. Then Shanks might tease Luffy about his still - crazy appetite. Luffy, in turn, could show off his new crew members to Shanks.
Nami could also be a common character. She might help Luffy manage the financial aspects of his admiral duties, as well as use her navigation skills to assist in any navy - related voyages. And of course, she'd be there to keep Luffy in check when he gets too carried away.
One characteristic is the blend of different power systems. Naruto has chakra - based ninjutsu while Luffy has his Devil Fruit powers. Fanfictions often explore how these powers interact. For example, in some stories, Naruto might teach Luffy about chakra control or Luffy might show Naruto how to be more carefree in battle.