She might convince him by showing him the long - term benefits for the village. For example, she could tell Naruto that in ANBU, he can prevent threats before they become major problems.
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.
In some fanfictions, Naruto might join Anbu because of Sakura to prove himself worthy of her. Maybe he thinks that by becoming an elite Anbu member, he can show her that he's strong and reliable.
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.
One challenge would be the secrecy. Naruto is used to being open and honest with his friends, but in ANBU, he has to keep things hidden. Another is the new type of missions. He may not be used to the stealth and assassination - type missions that ANBU often undertakes.
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.
The Anbu sister could be a powerful and mysterious character. In the fanfiction, she might have unique abilities that Naruto is curious about. Their meetings could be filled with tension at first, as the Anbu are often secretive. But as Naruto's friendly nature breaks through, they start to share their stories.
One possible fanfiction could be about Naruto forming an unexpected bond with Kurenai's sister who is in the Anbu. Maybe Naruto stumbles upon her during a mission and they start to work together, gradually learning about each other's pasts and dreams.
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.
Naruto's personality might become more reserved initially. The Anbu experience often makes ninjas keep their emotions in check. So, he might not be as boisterous as the original Naruto. For Sasuke, he could be more on edge around Naruto. He would sense the change in Naruto and feel pressured to keep up. Sakura might become more cautious too. She would see the more serious side of Naruto and might try to be more like him in terms of being focused during missions.