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.
Well, in some versions, it might start with Team 7 being shocked at first. They may initially doubt Naruto's ability to be in ANBU because they still see him as the goofy Naruto they've always known. But as they see him in action, they start to respect his new role more. Maybe Naruto has to keep some secrets from them initially which causes some tension within the team, but eventually, they come to accept and support his position in ANBU.
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.
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.
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.
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.
Another factor could be the toll it took on his mental health. The ANBU often deals with dark and difficult missions. Naruto, with his positive and somewhat naive outlook on life, might have been affected more than others. He could have started showing signs of not being able to cope, and as a result, they forced him out to protect him from further harm.
You can find 'Naruto Anbu Fanfiction' on websites like Fanfiction.net. It has a large collection of fan - made stories about Naruto, including many focused on the Anbu. Another good place is Archive of Our Own (AO3). There are some really creative and well - written Anbu fanfictions there.
In the ANBU after leaving Team 7, Naruto will be confronted with numerous challenges. Physically, the missions are likely to be more intense, requiring him to further develop his skills and combat abilities. He'll need to learn new stealth techniques and master different types of weapons. Emotionally, he'll face isolation. ANBU work is solitary, and Naruto, who thrived on the camaraderie of Team 7, will have to adjust to being alone most of the time. Additionally, he'll be faced with complex political situations within the ANBU organization. He'll have to navigate through power struggles and different factions, all while trying to stay true to himself and his values.
Well, another option could be to check out Naruto - related forums. There are often fans who share their favorite fanfictions. Maybe post a request asking for a fanfiction where Naruto finds a secret ANBU - related thing. Some well - known forums are NarutoForums and Reddit's Naruto subreddit.