Well, one possible plot development could be Naruto joining the ANBU to seek revenge for Asuma's death. He might use the ANBU's resources and training to become stronger and hunt down those responsible.
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.
Well, in a fanfiction where Naruto joins ANBU, his training would intensify. He'd be trained by some of the toughest ANBU veterans. His skills in combat would become more refined as he'd learn to use weapons like kunai and shuriken with more precision. He may also develop new jutsu that are more suitable for covert operations. His growth as a ninja would be different from the regular path, focusing more on secrecy and assassination if required.
In this kind of fanfiction, one possible plot development could be Naruto having to deal with the secrecy aspect of ANBU. He might struggle with the morally grey missions they undertake. For example, he could be sent to spy on an old acquaintance. Naruto, being Naruto, might try to find a more positive solution to the situation rather than blindly following orders.
One possible plot could be Naruto facing the internal politics of ANBU. He might struggle to adapt to their more secretive and sometimes morally gray operations compared to his usual straightforward ninja way. For example, he could be assigned to a mission where he has to spy on a former ally, creating an internal conflict within him.
One possible plot could be that Kurenai has some sort of influence on Naruto's decision. Maybe she sees his potential in a different way than others. She could encourage him to join ANBU to better protect the village and its people. Naruto, being influenced by her words and perhaps having a sense of admiration for her, decides to take on the challenge of joining ANBU.
Well, one major plot change could be in the power dynamics. Since Naruto in Anbu is likely more skilled and experienced. He might take a more dominant role in Team 7's missions. For example, he could quickly assess and handle dangerous situations that the original Team 7 might struggle with. This could also change the relationships within the team. Sasuke might be more competitive towards Naruto, seeing him as an even greater rival. And Sakura might have more admiration or fear towards Naruto because of his Anbu status.
In this fanfic, Naruto might face tougher and more secretive missions. He could be trained in new and deadly ninja techniques specific to ANBU. Also, his relationships with other characters might change. For example, he might become more distant from his old friends as ANBU work often requires secrecy.
Well, in such a fanfiction, perhaps Naruto has just lost Sasuke again and is deeply depressed. The ANBU, seeing his skills and his need for a distraction, recruit him. He starts off being a bit of a misfit in ANBU, not following all the rules because of his independent nature. But as he continues, he starts to understand the importance of their work. He might even form new bonds with his ANBU comrades, which slowly help him come out of his depression.
In such a fanfiction, the plot could involve Naruto being constantly overlooked by the village. Fed up with this, he decides to join ANBU to prove his worth. He might face challenges like distrust from his ANBU comrades at first because of his reputation. But as he goes on missions, he shows his skills and determination, gradually earning their respect and changing their perception of him.
In this fanfiction scenario, Naruto joining ANBU after the Chunin Exams could lead to a major shift in his relationships. His friends like Sasuke and Sakura might not understand his decision at first. Naruto could gain access to new and powerful jutsu within ANBU. Also, he might face internal conflict as the ANBU's sometimes morally gray missions could clash with his own values of protecting everyone and being a hero in the traditional sense.