Nami might be shocked at first. She'd probably look at Luffy with wide eyes, not believing what she just heard. After all, Luffy is not the most romantic or traditional suitor.
The crewmates would have a range of reactions. For one, they trust Luffy's ability to handle himself, but they'd also be eager to reunite with him. Luffy's impulsive nature often leads him into adventures, and this time it's in a whole new world. The more level - headed ones like Nami and Robin would be thinking of strategies to either bring him back or join him. The fighters like Zoro and Sanji would be prepared to defend Luffy against any threats in this new and unknown Naruto world. And the rest of the crew would contribute in their own unique ways, whether it's through humor like Brook or scientific exploration like Franky.
They might be shocked. Luffy's Gear 5 is such a powerful and strange form. In the fanfiction, characters could be amazed at his new abilities, like his cartoon - like movements and seemingly limitless power.
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 She might become more withdrawn and serious, as Luffy was often the one to bring out her lighter side.
Nami would probably be shocked at first. She might worry about how this would affect Luffy's journey to become Pirate King. But then she would likely start thinking about practical things like how to take care of the baby on the ship. Sanji would be over the moon, seeing it as an opportunity to cook for a new little life. He might also be a bit jealous that it's Luffy and not him having a baby with Hancock.
Blackbeard's crew is also a diverse bunch. His more aggressive members like Burgess might be eager to start a fight with Luffy's crew. However, some of the more cunning members could be thinking of ways to use the situation to their advantage. They might try to manipulate Luffy or his crew into making mistakes. And if Blackbeard decides on a certain course of action, his crew would generally follow, but there could be some internal dissent depending on the situation.
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 characters' reactions can be quite diverse. Chopper would be extremely worried and immediately start his medical examination. He'd be constantly checking Luffy's symptoms and trying different remedies. Nami would be worried too but also thinking about how this could affect their journey and the crew's safety. Zoro might seem nonchalant on the outside but would be secretly on high alert, ready to fight off any danger. Sanji would cook up all kinds of nutritious food to help Luffy get better.
Most of the crew would be excited to meet the people who brought Luffy into the world. They would see it as an opportunity to understand Luffy better. Chopper might be a bit shy at first but would soon warm up and start asking a million questions about Luffy's early life, like what kind of diseases he had as a kid or how he grew up so strong.