One possible plotline could be Naruto using his modern knowledge and skills to change past events for the better in the Hidden Leaf Village. For example, he might prevent certain tragedies or help train the younger versions of his friends more effectively.
Well, perhaps Naruto is summoned during a crucial battle in the past. He could use his advanced jutsu, like the Rasengan variations he developed as Hokage, to turn the tide of the battle. This would not only show his power but also how the past and present are intertwined in this fanfiction. And he might also face the challenge of not disrupting the timeline too much while still achieving his goals.
In this fanfiction, Naruto being summoned to the past might also lead to some interesting character interactions. He could meet his parents when they were young. He might share his experiences with them, and in turn, learn more about their hopes and dreams. This could create a very emotional and heart - warming storyline. Also, his presence in the past could inspire some characters to strive for different goals, thus changing the future in unexpected ways.
He would probably use his leadership skills. Naruto has grown into a great leader as Hokage. In the past, he could quickly assess situations and lead others, whether it's in a battle or in village - building activities.
One possible reason could be the overwhelming stress. Being Hokage means handling a lot of political, social and security issues in the village. Naruto might just feel that he can't take it anymore and decides to quit in the fanfiction. For example, dealing with the constant threats from other villages and internal disputes within Konoha can be mentally and physically exhausting.
One possible plotline could be Naruto using his newfound time - traveling ability to prevent some of the major tragedies in the past. For example, he might try to stop the Uchiha massacre. He could also use his knowledge from the future to help his younger self become stronger faster, perhaps by teaching him some advanced jutsu he learned later in life.
One possible plotline could be Naruto as the 6th Hokage facing a new threat to the village. Hinata, being his wife, supports him from behind the scenes. She might use her Byakugan to gather intelligence. Naruto, with his leadership skills and Hinata's support, unites the village to combat the enemy.
A plotline could be Naruto having to deal with the remnants of old enemies. Some of Orochimaru's followers might still be causing trouble, and as Hokage, Naruto has to stop them without using excessive force. He wants to show mercy but also protect the village. Another aspect could be Naruto working on the village's infrastructure. He realizes that a strong village isn't just about having powerful shinobi but also about having a stable and prosperous community. So he starts projects like building new schools for ninja training and improving housing for the villagers.
One possible plotline could be that Naruto is lured into a trap by the Akatsuki. They use his overconfidence against him. Maybe they pretend to have a hostage that Naruto wants to save, and when he arrives, they overpower him with their combined jutsu. Another could be that they manage to find a way to nullify his Nine - Tails chakra, leaving him vulnerable to their attacks.
One possible plotline could be that Naruto's wings make him an outcast in the village at first. People are scared or jealous of his unique feature. But as he grows, he learns to use his wings in combat, perhaps in a new style of ninja fighting that combines aerial maneuvers. He could also use his wings to reach places quickly during missions, giving him an edge.
Well, a plot could involve Naruto facing challenges related to his new identity as a Senju. There could be those who oppose him having the Senju blood, perhaps out of jealousy or fear of his growing power. He might have to prove himself worthy of the Senju name. Also, his friendship with Sasuke could take on a new dimension. Since Sasuke is an Uchiha, there could be an interesting dynamic between the two clans' legacies within their friendship. Naruto could use his Senju powers to try and bridge the gap between the Uchiha and the rest of the village, as the Senju were often associated with peace - building in the past.
One possible plotline could be that Hinata is under some sort of mind - control. Maybe an enemy uses a jutsu on her that makes her see Naruto as a threat to the village in a false way. So, she kidnaps Naruto to stop him from doing something she believes is harmful. But as the story progresses, Naruto tries to break through to her real self and free her from the mind - control.
One possible plotline could be that Serafall, perhaps influenced by some external force or a misunderstanding, turns on Naruto. Maybe she believes Naruto has some hidden agenda that endangers her or her world. So she starts to undermine Naruto's efforts and even plots against him directly.