Tsunade could be a key character too. If Sakura starts training under her, Tsunade can bring a lot of experience and wisdom to the story. Also, she's the Hokage, so she has to deal with any political or military threats that might come after the Chunin Exams.
Obviously, Naruto himself. He's the main character and after the Chunin Exams, he's likely to be at the center of most of the action. His growth and development will be a major focus.
Sasuke is also very important. His actions and decisions, especially if he's still on the path of seeking power, can greatly influence the story. His relationship with Naruto will continue to be a driving force in the plot.
He might kill an enemy shinobi from another village. For instance, if there is a particularly aggressive and cruel shinobi from the Sand Village during the Chunin Exams who poses a great threat to Naruto's friends or the Leaf Village in general, Naruto could be forced to kill him in self - defense or to protect others.
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.
Chakra chains in Naruto fanfiction during the Chunin Exams could potentially be used as a unique form of attack or defense. Maybe a character has developed a special jutsu involving chakra chains and uses it to gain an advantage in the exams, like for capturing opponents or protecting themselves from attacks.
Obviously Naruto himself would be the main character. Sasuke could also play a key role. Maybe Sasuke is torn between his loyalty to the village and his friendship with Naruto. He might initially follow the village's decision but later realizes it was wrong. Another important character could be Jiraiya. If Naruto is abandoned, Jiraiya might take him under his wing more fully and train him away from the village.
Sasuke could still be a major rival. Even though they are friends, the competitive spirit between them might flare up again during the exams.
Well, the Mangekyou Sharingan could give a character a huge advantage in the Chunin Exams. It might allow them to see the moves of their opponents in slow motion, kind of like Sasuke's regular Sharingan but even more powerful. So they could easily dodge attacks and counter - attack.
It could be Orochimaru. He's always been interested in Naruto and has his own devious plans. He might frame Naruto during the Chunin Exams to create chaos and further his own goals of obtaining power and knowledge. Orochimaru could use his henchmen or his jutsu to make it look like Naruto is involved in some sort of treachery.
Obviously Naruto is one of the main characters. Since it's related to the Chunin Exams, his friends like Sasuke and Sakura are likely to be important as well. And the kage who is involved in the story would also be a main character, as they play a crucial role in Naruto's journey during the exams.
Naruto himself is obviously very popular. His journey through the Chunin Exams in fanfiction is often full of excitement and growth, so readers love to follow his story.
Naruto is definitely one of the most popular. His determination and growth during the Chunin Exams in the original series make him a natural focus in fanfiction. Sasuke is also very popular. His cool demeanor and powerful abilities draw a lot of attention. Sakura, as she evolves during the exams, is often a key character. Rock Lee with his unique fighting style and unwavering spirit is another popular choice. And Gaara, with his complex and somewhat dark personality, often features prominently in fanfiction about the Chunin Exams.