It could be a shinobi who has a personal vendetta against one of the Kages. He might use the Gokage Summit as an opportunity to get close to his target. This would make for a very intense and action - filled story as he tries to carry out his plan while avoiding detection.
A young and inexperienced ninja from a small village could be the main character. He could be sent to the Gokage Summit as an observer or a messenger. Through his eyes, the readers could experience the grandeur and the political complexity of the summit.
One possible plot could be a secret alliance formed among the Kages during the summit. They might decide to secretly work together against a new, powerful and yet unknown enemy that is threatening the ninja world. This would add an element of mystery and anticipation to the story.
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.
It could be Naruto himself. Since he has a connection to all the villages in some way, he could play a crucial role in the fanfic, perhaps as a mediator or someone who uncovers a hidden conspiracy during the summit.
Naruto could still be the main character. As the Hokage, he would be at the center of the Kage Summit. His ideals of peace and unity would play a major role in the interactions with the other Kages. He might try to convince the other Kages to support a new initiative for a more united ninja world.
The main characters are Naruto and Mei. Naruto is from Konoha and is known for his determination and strong will. Mei is from Kirigakure and is a powerful kunoichi. In this fanfic, they are likely to be at the center of the story, with their actions and decisions driving the plot forward.
It could be a rogue ninja who has a vendetta against all the villages represented at the summit. He might have been wronged in the past by the combined actions of the five great villages and now seeks revenge. He could use the chaos of the summit to launch attacks and try to undermine the stability of the shinobi world.
A possible plot might involve Naruto representing Konoha at the summit with Mei from Kirigakure. Maybe there are some secrets that come to light during the summit. For example, a threat to both villages that was being hidden by certain parties. Naruto and Mei then team up to expose the truth and save their villages. Along the way, they learn about each other's leadership styles and grow to respect one another.
Naruto himself could be the main character in a Shinju fanfic. He has always been about finding new ways to bring peace and understanding. His connection to the nine - tails could play an interesting role if he were to interact with the Shinju. Maybe he could try to convince the Shinju that the ninja world has changed and it doesn't need to be a source of fear and destruction.
Sasuke Uchiha could be a great choice as the main character. He already has a complex backstory and a lot of room for character development. His journey from seeking revenge to finding his own path in the Naruto series can be further explored in a fanfic.
It could be an original character. Maybe a young ninja who discovers their forging abilities by accident. They might come from a small, unassuming clan that has kept the forging secrets hidden for generations. This character would then have to navigate the Naruto world while keeping their newfound power a secret at first, until they realize they can use it to make a difference.