His relationship with Sasuke would be interesting. Sasuke might be initially suspicious of Naruto's decision to join such a secretive group. But Naruto could convince Sasuke that he's doing it for the greater good of the village and the ninja world, and they could end up working together on some behind - the - scenes missions.
With his friends like Sakura, Naruto's relationship would shift. Sakura might worry about Naruto getting involved in dangerous and morally ambiguous tasks in ANBU. Naruto would have to reassure her that he can handle it and that he's still the same Naruto at heart. Also, his friendship with other Konoha 11 members would change as they may not be as involved in his day - to - day life now that he's in ANBU.
If Naruto joins ANBU after the war in fanfiction, his personality would experience a significant shift. His once boisterous and outgoing nature might be replaced by a more stoic and calculating one. He would need to be more discreet in his actions and words. The trust - building that he was so used to in his normal ninja life would be different in ANBU. He would have to be more guarded about who he trusts, which could make him seem a bit colder on the outside. But deep down, his kind heart would still be there. He'd just be more careful about showing it, as ANBU's world is full of deception and he can't afford to be too naive.
He'd become more reserved. The ANBU environment is secretive and doesn't encourage open emotions. Naruto, who is usually so exuberant, would have to hold back. For example, he couldn't go around shouting about his dreams as freely as before.
His relationship with Sasuke would become even more complex. Sasuke might see Naruto's joining of Akatsuki as a betrayal or a sign that Naruto has finally given up on Konoha. Naruto's old friends in Konoha, like Sakura and Kakashi, would be very confused and hurt. They might try to bring him back, but also be wary of his new Akatsuki ties. And within Akatsuki, Naruto would have to navigate relationships with members who have different motives and personalities, some of whom might not trust him at all.
With his Anbu comrades, Naruto's emotionless state would create a sense of distance. They would find it hard to trust someone who doesn't show any emotions. However, some might respect his cold - efficient way of handling missions. In the long run, if he doesn't change, he might be isolated within the Anbu ranks, as relationships in the Anbu are also based on some level of mutual understanding and emotional connection.
His relationship with Sasuke would become more complex. Since they are from different villages now, there would be a new dynamic. Sasuke might see Naruto's move as a betrayal to Konoha at first. But Naruto's intention could be to bridge the gap between the two villages for Sasuke's sake too.
If Naruto joins ANBU after the war in fanfiction, it could lead to some interesting character developments. He would have to deal with the darker side of the ninja world that ANBU often encounters. This might make him more cynical or, on the contrary, he could try to change ANBU from within. He'd be able to use his Uzumaki powers and his Sage Mode in more covert operations, which would give Konoha a huge advantage. Also, his relationship with other ANBU members would be complex. Some might respect him immediately because of his war hero status, while others might be skeptical of his more open - minded and friendly ways.
He would likely become more withdrawn. Naruto is usually so open and exuberant, but heartbreak could make him close off. In ANBU, he might be quieter, more focused on the mission at hand. He'd still have his determination, but it would be a more solemn determination. His sense of humor might also disappear for a while as he copes with his pain.
His relationships would become more complex. He'd have to start from scratch with new people. Some might be friendly right away, while others could be hostile.
He would likely become more secretive. Since ANBU operates in the shadows, Naruto would have to keep a lot of things to himself, which is a big change from his usually open - minded self. Also, the death of Asuma could make him more ruthless in combat, as he realizes the harsh reality of the ninja world. He may still hold onto his core values of protecting his friends and the village, but his methods could be more extreme in the ANBU.
His character could change in several ways. Firstly, he'd likely become more stealthy. In the ANBU, being able to move without being detected is crucial. Also, he might become more cynical. The ANBU deals with some dark stuff, and that could make Naruto question the world around him more. He may still hold onto his core values of protecting his friends and the village, but he'd view things from a more jaded perspective. He'd also have to be more calculating in his actions, thinking several steps ahead like the other ANBU members.