If we swap Star and Marco, then the main antagonists could be those who were previously minor annoyances for the other character. For example, if Marco is now in Star's role, Ludo, who was a main antagonist for Star, could be an even bigger threat as Marco might not have Star's natural magical intuition to deal with him.
For the older generation like the Third Hokage, watching an AU fanfiction might make them regret some of their decisions in the original story. If they see an AU where they handled things differently and it led to better outcomes for the village and its people, they might feel a sense of remorse. This could then affect how they interact with the younger generation. They might be more open to new ideas and less set in their ways, which in turn could improve their relationships with the likes of Naruto and his friends.
Well, perhaps in this swap AU, their powers are also swapped. Star has Marco's karate skills enhanced to a supernatural level, and Marco can now use Star's wand and spells. Also, the relationships they have with other characters could be reversed. Their friends might react very differently to this new 'them'.
One great 'Female Naruto Shikamaru AU' fanfiction is 'The New Path'. In this story, the female Naruto has a completely different dynamic with Shikamaru. It explores how their relationship might develop in an alternate universe where Naruto is female. The characterizations are really well - done, staying true to the original personalities while also adding new twists due to the gender change.
He could meet an AU version of Hinata who is more assertive and outgoing. Maybe she's a powerful ninja in her own right and not as shy as in the original story.
He might be shocked. In the fanfic, if he sees things like his friends' future achievements or the new threats that emerge, it would surely startle him. For example, if he discovers that one of his friends has a family of their own and has become a great leader in the village, he would be proud but also a bit surprised at how much has changed.
With his usual determination. Naruto has always been one to face difficulties head - on. So, even if he's shocked by what he sees in the fanfic's future, he'll likely try to find solutions immediately.
One possibility is that Naruto enters an AU where chakra doesn't exist. Instead, there are other forms of power. He would have to learn how to use this new power from scratch. Also, the relationships between different ninja clans could be very different. Naruto might end up making new alliances and enemies based on this new dynamic. This could be a great opportunity for character development as he faces challenges that are completely different from what he's used to in his original world.
Naruto could be a tech geek in a modern AU, working on the latest software developments. Hinata might be a fashion designer. They could meet at a tech - fashion event where Naruto is presenting some new wearable tech and Hinata is looking for inspiration for her new collection. Their relationship would be a blend of two different worlds, with Naruto being amazed by Hinata's creativity in fashion and Hinata being interested in Naruto's technological prowess.