Well, Naruto and Sasuke are the obvious ones. They are the main characters in the original series and their power levels and relationships are always a big part of any fanfic. But in Naruto God Tree fanfic, characters like Hagoromo and Hamura, the sons of Kaguya, could also be very important. They have a primordial connection to the God Tree as their mother was closely associated with it. Also, Orochimaru could be a significant character. His thirst for knowledge and his ability to experiment could lead him to be interested in the God Tree, and he could either be a villain or an unexpected ally in fanfics.
Naruto would likely still be one of the most important characters. His role as a main protagonist in the original Naruto series means he'd probably play a crucial part in any fanfic with a 'destined to happen' theme, whether it's about fulfilling a new prophecy or saving the world in a different way.
Obviously Naruto is one of the most important. His strength and his ability to inspire others are crucial in the Fourth War setting. He's the one who can turn the tides with his positive attitude and powerful jutsu.
Other important characters could be the enemies they faced during that era. For instance, the ninjas from other villages they fought against in the wars. These enemies could help showcase the Sannin's combat abilities and strategic thinking. Also, some of their comrades from Konoha, like Kakashi's father Sakumo Hatake, could be included to add more depth to the story.
Naruto himself is likely to be very popular. His unique personality and powerful ninja abilities make him a standout. People would be interested to see how he fares in the DxD universe.
Naruto himself is the most obvious one. Since it's a Naruto - related fanfic, he would likely be at the center of any crossovers with god - like entities. His strong will and desire to protect his village make him a prime candidate for interacting with powerful gods.
Sasuke also plays a crucial role. His relationship with Naruto, whether it's one of friendship or rivalry in the end of the fanfiction, can shape the overall story. He has his own journey of redemption or further descent into darkness, depending on the plot.
Naruto Uzumaki is of course the most important. He is the main character, and the whole story revolves around his growth, from an outcast in the village to a great Hokage.
Naruto Uzumaki is the most important character. He is the protagonist, and the whole story revolves around his journey to become Hokage. Sasuke Uchiha is also very important as Naruto's rival. And Kakashi Hatake, who is Naruto's teacher, plays a significant role in guiding Naruto and his friends in their ninja training.
The ancestors are usually important as they are the starting point of the family line. Also, the first - born in each generation might be significant.
Obviously, Naruto is the main character. He is the one who becomes this 'god - like' figure in the fanfic. But there are also other important characters like Sasuke. Sasuke might play a role in either supporting Naruto's new power or being in conflict with him because of it.