Well, their relationship could be super interesting. Naruto is from a world of ninjas and Luffy is a pirate. Naruto might teach Luffy some ninja tricks like stealth. And Luffy would show Naruto the joys of the open sea and adventure. They'd probably support each other no matter what. For example, Naruto could use his shadow clones to help Luffy in a fight on his ship, and Luffy would use his stretchy powers to get Naruto out of a tight spot in a ninja battle.
One possible adventure is that they go to a mysterious island that is said to hold the secrets of both ninjas and pirates. This island might be filled with dangerous traps and powerful guardians. Naruto would use his speed and strength as a ninja to navigate through the traps, while Luffy would use his rubber body to protect them from any physical attacks. They would also meet other characters from both universes on this island, and together they would try to uncover the secrets of the island.
Naruto's ninjutsu and Luffy's devil fruit powers would interact in really cool ways. For instance, Naruto could use his wind - style jutsu to enhance Luffy's attacks, making his Gum - Gum attacks even faster and more powerful. Luffy's ability to stretch could help Naruto reach enemies that are far away or in hard - to - reach places when he's using his Rasengan.
If they were brothers in a fanfic, their adventures would be full of humor too. Imagine Luffy trying to eat Naruto's ramen and Naruto getting all protective. They'd travel to different worlds, maybe even visit the One Piece world's islands and the Hidden Villages in Naruto's world. Their different personalities would create interesting situations. Naruto is determined and a bit hot - headed, while Luffy is carefree and always hungry. Together, they'd face many challenges and make new friends along the way.
Well, 'Fem Luffy: The Brothers' Shield' is also worth checking out. The overprotective nature of the brothers is really emphasized in this one. They go to great lengths to keep fem Luffy safe, which leads to some really intense and emotional scenes. It's a great read for those who like this kind of fanfiction.
Often, the Marines can be main antagonists. They see pirates as a threat, and with Ace and Luffy being pirates, they would be constantly on the Marines' radar. Marines like Akainu are especially dangerous, as his extreme sense of justice could lead to direct confrontations with the brothers.
One common theme is family loyalty. The overprotective brothers, like Ace and Sabo, are always there for Luffy because of their strong family bond. Another theme is the conflict between protection and freedom. Luffy is an adventurous spirit and his brothers' overprotectiveness can sometimes limit his freedom, which leads to some interesting plot developments.
A good fem Luffy and overprotective brothers fanfiction should have strong characterizations. The brothers' overprotectiveness should be believable and not overdone. For example, they might be protective because fem Luffy is a female in a dangerous pirate world. Also, the story should have an engaging plot. Maybe fem Luffy is trying to prove herself despite her brothers' protectiveness.
Another storyline could revolve around a time when they got separated in a dangerous area, like a mysterious island full of ancient traps. They both have to find their way back to each other while overcoming various challenges. Luffy might make new friends who help him, and Ace might discover some secrets about their family history in the process.
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.