Shanks might interact with Luffy's crew in a very friendly and father - like way. He could pat the crew members on the back, give them words of encouragement, and share his experiences with them.
If a marine joins Luffy's crew in a fanfic, it could be quite interesting. At first, there might be a lot of distrust among the crew members. After all, they've been fighting against marines for a long time. But if the marine has a strong sense of justice that aligns with Luffy's own view of right and wrong, they could gradually be accepted. For example, the marine might bring in some new combat techniques or knowledge about the navy's operations that could be useful to the Straw Hats.
Zoro would be deeply affected. He has sworn to follow Luffy and his death would be a huge blow. He might feel like he failed in his duty to protect the captain. He would likely become more withdrawn at first, but then focus on getting stronger to avenge Luffy if there was someone to blame for his death.
Naruto's abilities would bring a new flavor to Luffy's crew. His chakra - based powers are different from the Devil Fruits and Haki in One Piece. His healing ability, if he has learned some medical ninjutsu, could be crucial for the crew. Also, his summoning jutsu could call forth some powerful creatures to aid the crew in tough battles. For instance, if he summons a giant toad, it could be used as a distraction or a battering ram against enemy forces.
Naruto's upbeat and positive personality would mesh well with the crew. He and Luffy could become great friends due to their similar energetic natures. Naruto's tendency to be a bit of a goofball would also blend in with the light - heartedness of the Straw Hats.
I think it has the potential to be very engaging. A marine joining Luffy's crew would bring in a clash of ideologies and force both the marine and the crew to adapt and grow. It could lead to some unexpected plot twists and character developments.
Fem Luffy would probably bring a lot of energy. She might be more empathetic in some ways compared to the original Luffy, which could help in resolving internal crew conflicts. For example, if two crewmates have a disagreement, she could use her charm and understanding to smooth things over.
Obviously, they will support Luffy all the way. He is their captain, and they have complete faith in him. They have been through so much together, and they know Luffy's strength and determination.
Imagine Luffy ate a devil fruit that gave him the power to control minds. This would be a very different power compared to his current Gum - Gum abilities. His crew would have to trust him completely not to abuse this power. There could be ethical discussions within the crew. Also, in terms of leadership, Luffy might have an easier time getting others to follow his plans, but it could also create some tension if the crew felt he was relying too much on his mind - control powers instead of his natural leadership qualities.