It could be a powerful pirate crew that has a vendetta against either Luffy or Sabo. Maybe they have some history with the Straw Hat Pirates or Sabo's group.
Luffy, of course. He and Sabo have a deep history. They grew up together and Sabo was like a brother to him. Their reunion would be filled with joy, hugs, and probably a lot of tears. Luffy would be over the moon to have Sabo back in his life and on his ship.
In a 'Sabo meets Luffy crew' fanfiction, there could be a lot of emotional reunions. Sabo might share his adventures since they last parted. He could train with the crew members, especially Zoro to exchange sword - fighting skills. And he would surely have a great time reminiscing about their childhood with Luffy.
One interesting scenario could be that they team up against a powerful new enemy. They combine their unique skills, Luffy's rubber abilities and Sabo's fire - based attacks, to create a formidable force.
One possibility is that they would first be confused by each other's strange abilities. Naruto with his jutsus, and Luffy and Sabo with their Devil Fruit powers. But then they might find common ground in their strong sense of loyalty and friendship. They could team up to fight against a common enemy, perhaps some powerful pirates or shinobi who are causing chaos in both their worlds.
Naruto is very energetic and loud in his own way, much like Luffy. So they might blend well in terms of their exuberance. However, Naruto can be a bit more impulsive when it comes to protecting his friends, while Sabo is more level - headed. This could lead to some clashes as Sabo might try to think things through more carefully. But at the same time, Sabo could also learn from Naruto's spontaneity. Luffy's carefree nature might initially seem strange to Naruto, but Naruto could also be drawn to Luffy's unwavering belief in his dreams.
Typically, Sabo x Luffy fanfiction emphasizes their strong brotherly bond. It often showcases their loyalty to each other. Many stories also explore their shared dreams and how they support one another in achieving those dreams.
One great 'Ace Sabo Luffy Fanfiction' is 'The Brothers' Bond'. It beautifully explores their relationship, showing how they support each other through various challenges. Another one is 'Sabo's Return'. It focuses on Sabo coming back into Luffy and Ace's lives and how they all readjust. There's also 'Ace and Luffy's Adventure', which takes the three on a fictional journey filled with action and heartwarming moments.
Well, one possible future for them in Marine fanfiction could be that they form a special unit. Ace with his fire power, Luffy with his rubber abilities and Sabo with his skills would be a formidable team. They could be sent on special missions to deal with the toughest pirates. This way, they are still following their dreams of adventure while being part of the Marines.
Well, it could be that in certain fanfictions, the writers are trying to explore 'what - if' scenarios where Ace and Sabo have some sort of falling out with Luffy. It might be because of jealousy, perhaps they think Luffy is getting more attention or something. But really, this is a huge departure from their normal loving relationship in the main One Piece story.