Well, as of the latest manga chapters, Yamato has indeed become a part of the Straw Hats. This decision brings new dynamics and adventures to the crew.
Kizaru could also be interesting. His light - based powers are extremely powerful. If he joined the Straw Hats, he could use his speed and laser - like attacks to protect the crew. However, he would need to change his loyalty from the World Government, which could create a complex and engaging storyline.
One idea could be that Law brings his medical skills to the crew. He could teach Chopper some advanced medical techniques from his own knowledge and experiences. For example, he might introduce new ways of treating certain rare diseases that are common in the Grand Line but unknown to Chopper. Another plot could revolve around Law's devil fruit powers. He could use his Room ability in creative ways during battles to protect the Straw Hats or to come up with unique battle strategies in combination with the other crew members' abilities. Maybe he creates a huge 'Room' that encompasses the entire ship during a sea battle, allowing the Straw Hats to move around freely while their enemies are trapped or disoriented.
It could be Chopper. Since Chopper is a doctor and Reiju has some medical knowledge, they might bond over sharing medical techniques and treating the crew's injuries. Also, Chopper's kind - hearted nature would make him a great friend for Reiju who might be used to a more cut - throat family environment.
If Naruto was raised by the Straw Hats, he'd probably be a very different person. He might be more carefree like Luffy. For example, he'd be used to the wacky adventures on the Grand Line. His ninja skills could blend with the pirates' combat styles, creating some really unique fighting techniques.
He might become more relaxed. The Straw Hats are a very laid - back and fun - loving crew compared to Law's more serious group. So, being around them, Law could start to crack jokes more often and not be so uptight all the time. For example, he might start to participate in Usopp and Luffy's silly games on the ship.
His personality would become more outgoing and adventurous. The Straw Hats' lifestyle is full of exploration, so Naruto would be more eager to take risks.
I really like the fanfiction where the Straw Hats time travel to the future. In this story, they see how their actions have affected the world in the long run. It shows a post - apocalyptic world that was caused by a series of events that they were unknowingly a part of. It makes them reflect on their current actions and how they can change things for the better. Another good one is the one where they go back to the time of Gol D. Roger. They get to meet the legendary pirate and learn some of his secrets, which is really exciting for fans of the series.