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.
She could be a former pirate captain herself. Maybe she was one of the most feared pirates in her time, and her skills and reputation were passed down to Luffy in some way, even if he didn't know it was from his mother.
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.
In a fanfiction where Luffy meets Roger, it could be an amazing encounter. Roger might see in Luffy the same spirit of adventure and freedom that he had. He could pass on some hidden knowledge about the One Piece or give Luffy a cryptic hint about the true nature of the Grand Line. This meeting could also inspire Luffy even more, fueling his determination to become the Pirate King. It would be a moment full of emotion and significance for both characters and for the entire One Piece universe.
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.
Well, in such a fanfiction, Luffy might gain some valuable advice from Roger. Maybe Roger could share his experiences about the One Piece and the Grand Line, which would inspire Luffy further in his journey to become the Pirate King.
A possible plotline could be a battle scenario. Maybe there's a powerful enemy threatening both Luffy's crew and Marco's group. So they meet on the battlefield and have to quickly figure out how to work together. Their different fighting styles, Luffy's Gum - Gum powers and Marco's phoenix - related abilities, make for an exciting combination in combat.
Well, it could be that Luffy tries to recruit Whitebeard into his crew. Luffy is always on the lookout for strong allies, and Whitebeard with his immense power would be a great addition. However, Whitebeard might laugh it off, seeing Luffy as a young and brash pirate with big dreams but still a lot to learn.
In this fanfiction, Luffy might initially be in awe of Whitebeard. He could be eager to learn from the great pirate. Maybe they'll team up for a short adventure against a common enemy, like a powerful marine force. Luffy's energy and Whitebeard's experience could make for an interesting dynamic.