Nami would probably be devastated. She has been with Luffy through so much, and his death would be a huge blow. She might become more withdrawn and serious, as Luffy was often the one to bring out her lighter side.
It would be a wild combination. Vegeta's serious and prideful nature would contrast with Luffy's carefree attitude. But his combat skills would be a great asset. He could probably take on the toughest enemies easily. He might not get along well with Usopp at first because of Usopp's cowardly tendencies, but over time, he could teach Usopp to be braver. And his presence would make the Straw Hat crew even more feared among their enemies.
The order in which the main characters of One Piece joined the Grass Hat Pirates was as follows:
1 Monkey D Luffy
2 Nico Robin
3 Franky
4 Choba (Chopper)
5 Brook
6 Sauron (Sengoku)
7 Nami
8 Usopp
9 Sanji
10 Nico Robin's father
The above are the original members of the Hat Pirates. As the plot developed, Luffy, Nami, Usopp, Sanji, Sauron, Choba, and Franky joined one after another. Nicole Robin also joined the Hat Pirates at some point later.
Another scenario could be that Hancock's presence causes some internal conflict within the Straw Hat crew. Nami might be a bit wary of her because of her past actions and power. Chopper could be curious about her Devil Fruit abilities. Zoro might not trust her easily. However, in the face of a common enemy, they would have to put aside their differences and work together. Hancock might learn a lot from the Straw Hat crew's camaraderie and freedom - loving spirit, which could change her perspective on pirates in general.
For the Straw Hat crew, it would be a major shift. Sanji would be beside himself with excitement, always eager to please and protect. Zoro would have a complex reaction. He might be a bit more gentle in his challenges to her but also be on high alert to make sure no one takes advantage of her. Nami would be thrilled to have a female companion on board. She could teach Luffy about things like haggling in a more feminine way. Usopp would be the one to spread the news around the ship in his own humorous way. Chopper would study if there are any health differences for a female Luffy. Franky would be focused on making the ship more comfortable for her, like adding softer seating areas. Brook would be using his skeletal charm to make her laugh and keep the crew's spirits high.
Well, Naruto's skills like his shadow clones could be a great asset. He could use them for various tasks on the ship, from cleaning to helping in battles. His determination would also match the Straw Hats' spirit.
The Straw Hat crew would probably be very surprised at first. Nami might worry about how Hancock's presence would affect their finances, since Hancock is used to a more luxurious lifestyle. Usopp would be in awe of Hancock's beauty and powers. Chopper would be excited to have Hancock around, as she could potentially teach him about different kinds of medicine from Amazon Lily. Zoro might be a bit skeptical at first but would come to accept it as long as Luffy was happy.
Luffy would probably be excited. He loves having new and interesting people on his crew. Zoro might be a bit cautious at first but would come to respect Naruto's fighting skills. Nami would see Naruto as someone who could be useful for his abilities.
The crew's reaction would be mixed with shock and joy. Franky would start building baby - friendly gadgets and cribs for them. Brook would be playing soothing music for Robin and Zoro to keep them relaxed. At first, some of the crew might be worried about how this would affect their adventures. But overall, they would come together. For example, Zoro's tough - guy image might change a bit, and the crew would tease him good - naturedly. Robin, being the more reserved one, might be a bit embarrassed by all the attention at first, but she would appreciate the love and care from the crew.
One idea could be that the Straw Hat Crew travels back in time to the era of the Pirate King Gol D. Roger. They could meet him and learn some of his secrets, or even witness some of his greatest battles. Another plot could involve traveling to a time when the world was in a different state, like before the Grand Line was discovered, and they have to adapt to a whole new set of challenges and rules. Maybe they accidentally change something in the past that has a huge impact on the present and they have to figure out how to fix it.