The main characters would probably start with Naruto. He's the protagonist of the Naruto series and his presence in a 'naruto wave kage fanfic' would be natural. The Kage are key figures, for sure. But we can't forget about characters like Zabuza and Haku who had a big impact on the Wave Village story originally. They could be resurrected or their backstories could be further explored in relation to the Kage in the fanfic. And there could be new, original characters created specifically for the fanfic who are from the Wave Village and interact with the Kage in interesting ways, like a young ninja from the Wave Village who has a special power that catches the attention of the Kage.
In a 'naruto wave kage fanfic', Naruto is almost always a main character due to his significance in the Naruto universe. The Kage are also central as they represent the leadership of their respective villages. The Wave Village might introduce characters like Tazuna or Inari as main characters too. Tazuna was important in the original Wave arc in Naruto. His skills as a bridge - builder could play a different role in the fanfic, like being a symbol of hope for the Wave Village in a time of conflict involving the Kage. Inari, with his growth and potential, could also have a major part in the story, perhaps forming an unexpected bond with one of the Kage.
Well, a 'naruto wave kage fanfic' could center around the Wave Village and its connection to the various Kage. It might tell a story of how the events in the Wave Village impact the decisions of the Kage from different ninja villages. For example, it could be about how the actions of the ninja in the Wave Village during a crisis make the Hokage of Konoha take certain diplomatic or military actions towards other villages. It could also explore the backstories of the Kage characters in relation to the Wave Village, like if one of the Kage had a personal experience in the Wave Village when they were younger that shaped their leadership style.
The Kage Fujin is likely to be one of the main characters. They are probably a powerful figure with unique abilities related to the elements or some other special power.
In addition to Sasuke, Kakashi, and Sakura, other characters like Iruka sensei would be affected. Iruka was one of the first people to believe in Naruto. Naruto's death would be a huge blow to him. Also, the villagers of Konoha who had started to see Naruto in a new light might have to re - evaluate their views. And characters in the Land of Waves, like Tazuna and his family, who had come to rely on Naruto's help, would also be impacted. They might lose hope or face greater danger without Naruto there to protect them.
The Hokage, like Tsunade or Kakashi, could be the ones training Naruto. They know Naruto well and have a lot of knowledge and skills to pass on.
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.
The Kages themselves are often main characters. For example, Tsunade from Konoha, Gaara from Suna, and the other village leaders. They play important roles in the political and power - related discussions during the summit.
Obviously Naruto would be one of the main characters. And probably characters from the Wave like Tazuna would also be important as Naruto is ruling in the Wave.
A new, young ninja from a minor village could be the main character. They could be trying to make a name for themselves and their village at the Kage Summit. They might get involved in some political intrigue or even a fight between the Kages and prove their worth.
Naruto himself could still be the main character, but this time showing even more advanced kage - level skills. Maybe he's facing a threat that only his new and improved abilities can handle.
Since I don't know the specific fanfic, Sakura is likely one of the main characters as it's in the title. There may also be characters related to her, like her friends or family who are affected by her death in the wave.