Sakura is often overlooked but could be an interesting character to focus on. She was trying to prove herself as a strong shinobi during the war. You could write about her growth in medical ninjutsu during the war, and how she used it not only to heal but also to come up with new combat strategies. Also, her relationship with Sasuke and how it was affected by the events of the war could be explored in great detail.
Kakashi could also be a great focus. He had so many relationships and responsibilities during the war. You could show how he balanced his loyalty to the Leaf Village, his friendship with Obito (even in the midst of their conflict), and his mentorship of Naruto and Sasuke. Plus, his Sharingan abilities always add an interesting element to the story.
I think Obito could be really interesting. His complex backstory and his role in the war were so crucial. You could explore his internal struggle further, like his lingering feelings for Rin and how that influenced his actions during the war in more depth.
How about a rogue ninja who has his own motives during the Fourth Shinobi World War? He might not be on either side of the main conflict, but he has a personal vendetta against one of the powerful shinobi leaders. He could be constantly interfering in the battles, causing unexpected twists and turns.
One idea could be exploring the backstories of minor characters during the war. For example, how the war affected the normal villagers who were not shinobi. Another could be a story where a new, unexpected alliance forms between different ninja clans to fight a common, greater threat that was overlooked during the original war.
One interesting plot point could be Naruto's struggle with his new godlike powers. He might find it difficult to control them at first, causing some chaos on the battlefield. For example, he tries to heal a comrade but accidentally uses too much power and ends up giving them some sort of super - ability that they can't handle. Another plot point could be how the other shinobi react to his sudden transformation. Some might be in awe, while others might be jealous or even afraid.
I think Rock Lee. He's often overshadowed by the more powerful ninjas with special abilities like Naruto and Sasuke. But during the 4th Shinobi War, his sheer determination and hard - work - based fighting style could have been explored more. He could have had some really cool moments against the stronger opponents.
A civilian who somehow gets involved in the war and discovers they have latent shinobi abilities. They could start as a clumsy and inexperienced character but grow into a powerful force.
Rock Lee is often overlooked in some of the larger war - time stories. His unique taijutsu skills could be really interesting to explore in the context of the Fourth Shinobi War. He could take on some really tough opponents and show off his growth.
Xemnas. As the leader of Organization 13, he could bring a whole new level of villainy to the Naruto world. His plans and manipulations could create a large - scale conflict, and his power and charisma could make him a formidable foe for the Naruto characters. He might try to take over the ninja world using his own brand of dark magic or whatever powers he has in the Organization 13 lore.
One of the most heartbreaking scenes could be when his friends find out about Naruto's death. For example, Sakura, who has been with Naruto through so much, would be completely shattered. Her reaction of disbelief and then overwhelming grief would be really sad. Another scene might be when the whole village of Konoha hears the news. The silence that would fall over the village, with people just stopping in their tracks, would be a very poignant moment.
It could be an original character. For example, a young ninja from a small, unassuming clan that has been overlooked in the grand scheme of the war. But as the war progresses, they show extraordinary skills and courage, becoming a key figure in the battles.
Sasuke could also be the main character. His quest for power and revenge could be further explored in the context of the war. He might find himself in situations where he has to choose between his personal goals and the greater good of his village and the shinobi world.