Sasuke might be a bit jealous at first. He's always been competitive with Naruto, and seeing Naruto in a special and elite unit like ANBU could trigger that jealousy. He might try to prove that he's just as good or better. Sakura, on the other hand, would probably be worried. She cares a lot about Naruto and ANBU missions are often dangerous.
The reactions could be complex. Team 7 has a deep bond. They might feel left out that Naruto has this new part of his life that they don't fully understand. But also, they would be curious. They'd want to know what Naruto does in ANBU, how he trains, and what kind of missions he goes on. This could lead to them getting closer to Naruto as they try to learn more about his new role.
They might be quite surprised. Minato, for example, could be shocked to see how some fanfictions might depict his relationship with his students or his family. Kakashi might find some of the stories about his past quite interesting, while Obito and Rin could have various reactions depending on how they are portrayed in the fanfiction.
Maybe in the fanfiction, the ANBU Team 7 is sent on a mission to infiltrate a hidden organization that is planning to attack Konoha. Naruto uses his shadow clones in creative ways to gather intelligence. Sakura disguises herself as a member of the organization and uses her knowledge of poisons to take out guards silently. Sasuke uses his Sharingan to detect hidden traps and enemies. Along the way, they discover that there is a traitor within Konoha who is feeding information to the enemy.
You might consider adding Tenten to the team. She has a vast knowledge of weapons which could be handy in various missions. And Kiba, with Akamaru by his side, could offer enhanced senses and tracking abilities for the Anbu team.
It could be Orochimaru. He has always been interested in Sasuke and might target ANBU Team 7 to get to him. Orochimaru's experiments and his desire for power make him a formidable and menacing villain. He could also be using some new jutsu or have created more powerful minions to fight against Team 7.
Well, if Naruto and Sakura kiss in fanfiction, the reactions would be diverse. Fans who have been rooting for them, known as shippers, would likely be overjoyed. They would see it as a validation of their long - hoped - for relationship. However, fans of other pairings, like Naruto and Hinata or Sakura and Sasuke, might not take it so well. They might feel that it goes against the 'canon' in a way. Also, some more purist fans might think that it's too out of character for the original Naruto and Sakura. There are so many different perspectives within the Naruto fan community.
In a Naruto and Rin kissing fanfiction, the reactions would be diverse. Naruto might initially be caught up in the moment, but then have a flood of conflicting emotions. He could wonder how this would affect his relationship with his friends, especially those who knew Rin in a different context. For Kakashi, it could be a huge emotional blow. He might retreat into himself, or go on a quest to understand what led to this. The village elders might see it as a disruption to the social order. Among the fans, some would be excited by the boldness of the concept, seeing it as a chance to explore uncharted territory in the Naruto universe. Others would be critical, stating that it doesn't fit with the established personalities and story arcs of the characters. And then there are those who would be intrigued but also cautious, waiting to see how the writer develops the story further to either justify or retract this unexpected event.
He might form a mentor - mentee relationship with some of the ANBU members. They would be the ones guiding him in his training, so they would be like his teachers. Naruto would look up to them for their skills and knowledge.
Another plot could involve the Anbu team being tasked with protecting a young and powerful ninja from another village who has valuable knowledge. Along the way, they form an unexpected bond with this ninja and learn new techniques from them.
Well, it could be about Naruto secretly training to become an ANBU member. Maybe he has to hide this from his friends because the ANBU work is so dangerous and secretive.
Naruto might be heartbroken. He's a very emotional character, so he could cry a lot and feel a deep sense of loss.