Well, for a'shinobi clan wars naruto fanfic', it could be a new character. A young shinobi who was orphaned because of the clan wars and is now seeking revenge on the clans that started it all. Or it could be an old, wise shinobi from one of the most powerful clans who tries to use his wisdom to end the wars. Also, Hinata could be a main character, with her gentle nature trying to bring peace among the warring clans.
One possible main character could be a shinobi from a clan that has been marginalized in the past. They see the clan wars as an opportunity to gain respect for their clan. Another could be a female shinobi who is stronger than most of the male shinobi in her clan and is trying to change the patriarchal structure within the clan during the war. And Rock Lee could also be a main character, with his hard - work - pays - off attitude inspiring other shinobi to rise above the clan rivalries during the wars.
Naruto himself could be a main character, using his skills and influence to try and stop the clan wars. Another could be a young shinobi from a minor clan who has a special ability and wants to prove their clan's worth. And Sasuke could also be involved, perhaps having his own motives related to the clans.