The Bnha universe's reaction would be mixed. Those who are into complex stories, like Todoroki, might study the relationships in Hamilton fanfiction. But others, like Mineta, might not be interested at all because it doesn't have much to do with his usual interests. Overall, it would depend on the individual characters' personalities and interests.
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 He would likely become more withdrawn at first, but then focus on getting stronger to avenge Luffy if there was someone to blame for his death.
Some would be inspired. Characters like All Might might see Peter Parker's journey as similar to his own in some ways. Both are trying to do good in a world full of challenges. All Might could appreciate Peter's determination to protect his city despite having a normal life outside of being a hero.
For heroic - centric fanfictions, they would likely be disdainful. Since they oppose heroes, seeing stories that glorify heroes would annoy them. They might scoff at the idealized versions of heroes in those fanfictions.
Nami would be inconsolable at first. Luffy has always been there to protect her, and his sudden death would leave a huge void in her life. She would probably cry for days. As time passed, she would remember all the things Luffy taught her about courage and believing in oneself. Nami would start to take on some of Luffy's leadership qualities in a way. She would be more outspoken about her plans for the crew and more determined to see their dreams through. She would also keep Luffy's memory alive by telling stories of his adventures and his selfless acts to new people they meet on their journey.
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.