One possible plot twist could be that Naruto has to face an unexpected opponent during the Chunin Exams. Maybe a rogue ninja infiltrates the exam and targets Naruto specifically because of his Nine - Tails power. Another twist could be that the rules of the Chunin Exams are suddenly changed in the middle, forcing Naruto to adapt quickly. For example, they might add a team - vs - team battle where Naruto has to work with his former rivals.
Naruto's training would likely become more intense. He might focus on mastering new jutsus like the Rasengan variations. He could also train in stealth and strategy more, as those are important for a Chunin. For example, he could practice sneaking up on opponents and setting up traps.
In the fanfiction, after they become Chunin, they might be assigned on more difficult missions together. This would force them to rely on each other even more. They could have long conversations during these missions, discussing their past experiences, their families, and their dreams. Naruto might share his dream of becoming Hokage in more detail with Shikamaru, and Shikamaru could talk about his desire to make the village a better place using his intelligence. Through these shared experiences and conversations, their friendship would grow deeper.
The other competitors in the Chunin Exams could also be the audience. They would probably have mixed reactions, some might laugh at him while others respect his boldness.
Maybe he realizes the exam is too dangerous or he discovers some unfairness in it. In the original Naruto story, Naruto has faced many difficulties and moral dilemmas during the Chunin Exam. So in the fanfiction, similar situations might push him to quit.
Well, Naruto might use his new jutsu that he has been secretly training. He could surprise Gaara with his determination and growth. Maybe he'll finally break through Gaara's tough exterior and make him see a different way of life.
She might be heartbroken. Hinata, being a shy and sensitive person, would likely retreat further into herself. She may feel that all her efforts to be brave and show her feelings to Naruto have been in vain.
He might face disappointment from his friends and mentors. His friends who were also participating in the exam might feel let down, and his mentors, like Kakashi, could be concerned about his decision and how it will affect his future as a ninja.