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.
Well, the crew would probably be on the edge of their seats. Luffy is known for his unpredictable and powerful fighting style. Katakuro, on the other hand, has his own set of unique abilities. Maybe the crew would be cheering Luffy on, shouting words of encouragement. They might also be worried at times, especially when Katakuro gets the upper hand in some moments of the fight. It would be a very intense moment for them to watch.
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.
A marine who has a special ability or talent that the crew lacks. Maybe a marine who is really good at deciphering ancient texts or has a unique form of martial arts. They would be attracted to Luffy's crew because of their freedom - loving spirit. And once they join, they could use their skills to help the crew in their adventures, whether it's finding a hidden treasure or fighting against a powerful enemy.
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.
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 He would likely become more withdrawn at first, but then focus on getting stronger to avenge Luffy if there was someone to blame for his death.
In 'luffy vs kaido fanfiction', Luffy's growth and new abilities are often explored. He might develop new forms of his Gear powers to face Kaido. Kaido, being extremely powerful, forces Luffy to push his limits. Fanfictions may also focus on the intense battle scenes, with detailed descriptions of their attacks and counter - attacks.
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.
In this fanfiction, Luffy might be initially in awe of Whitebeard's presence. He could challenge one of the crew members to a friendly spar, like Ace perhaps. And they might share stories about their adventures at sea.