In this fanfiction, Ace might share his amazing adventures with Luffy's crew. He could show off his cool fire - based powers and tell stories about his time on the sea before meeting them.
In fanfiction, if Ace joins Luffy's crew, it would be an amazing addition. Ace's powerful fire abilities would make the crew even stronger in battles. He could also bring a different dynamic to the group, as he has his own personality and backstory. His relationship with Luffy would be a central focus, and we might see more brotherly bonding moments on the ship.
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 He would likely become more withdrawn at first, but then focus on getting stronger to avenge Luffy if there was someone to blame for his death.
If Ace joins Luffy's crew in fanfiction, his character could develop by becoming more of a team player. He's used to being on his own to some extent, but with the crew, he'd have to rely on others and they on him. His relationship with the other crew members would shape him, like learning patience from Chopper or strategy from Nami.
In a fanfiction, Ace's own experiences and battles could be related to Luffy's metabolism. Maybe Ace has some knowledge about a special fruit or power that could enhance Luffy's metabolism. He could share this with Luffy, leading to a new adventure where Luffy tries to obtain this thing to boost his metabolism. Also, Ace's death could have an impact on Luffy's metabolism. Luffy could go into a state of shock or extreme grief that either slows down or speeds up his metabolism in an unexpected way.
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.
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.