One great rival could be a character with a powerful Devil Fruit ability. For example, a character who has a Logia - type Devil Fruit that allows them to turn into a natural element like lightning. This would make them very difficult to defeat in combat as they could dodge attacks easily. They could also use their element - based powers to attack the Straw Hat Pirates in unexpected ways, such as sending bolts of lightning towards their ship.
A rival could be motivated by envy. The Straw Hat Pirates are known for their fame and the bonds they share. Another pirate or character might envy their camaraderie and the way they are able to overcome difficulties together. So, they want to break the Straw Hat Pirates apart and prove that their own way is better.
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 She might become more withdrawn and serious, as Luffy was often the one to bring out her lighter side.
They might have an epic celebration. The Straw Hats would be excited to see Shanks, especially Luffy. Luffy would probably challenge Shanks to a friendly duel or just be overjoyed to show him how far he's come. Shanks would be proud of Luffy and his crew, and they could all share stories of their adventures over a big feast.
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.
First, understand the Straw Hat Pirates' personalities well. For example, Luffy's carefree and determined nature. Then, create an OC (Original Character) that can interact meaningfully with them. Maybe the OC has a special skill or a unique backstory that ties into the pirates' adventures. Think about how the OC can join their crew or be an ally in their journey.
One popular trope is the 'lost relative' trope. For example, the OC could be a long - lost relative of one of the Straw Hat Pirates. Another is the 'powerful newcomer' trope, where the OC has some extraordinary power that helps the crew in a difficult situation. There's also the 'love interest' trope, although this can be a bit overdone. The OC might fall in love with one of the pirates or vice versa.
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.
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.
The members of One Piece's Grass Hat Gang were as follows:
Captain: Monkey D Luffy
Vice Captain: Nami
Third Helmsman: Usopp
Fourth Helmsman: Chopper
Fifth Helmsman: Robin
Sixth Helmsman: Franky
Helmsman Seven: Sanji
Eight Helmsman: Very flat (Y governance)