A really interesting plot could be Naruto traveling back in time to the era before he was born. He could meet his parents and other important figures in the village's history. This would give him a chance to understand the roots of the village better and also learn some new jutsu or strategies that he could bring back to his own time to make the Hidden Leaf even stronger as a Hokage.
One aspect that could be explored in Naruto Seventh Hokage cross - fanfiction is his leadership skills in new and unexpected situations. For example, he might be thrown into a parallel universe where the ninja world has different rules and he has to adapt his leadership style accordingly. Maybe in this universe, the villages are not as united as in his own, and he has to find ways to bring them together.
In fanfiction, Naruto as the Seventh Hokage might also face some personal growth challenges. He has achieved his childhood dream, but now he might feel a sense of emptiness or wonder what's next. Some fanfictions could explore his spiritual journey. Maybe he goes on a solo mission to find a deeper meaning in his life and his role as Hokage. Or he could be trying to bring about a new era of ninja technology in the village, using his influence to encourage innovation in areas like medical ninjutsu or new types of jutsu development.
Rock Lee. He's often overshadowed by the main characters but he has a lot of potential. In a fanfic, he could be Naruto's right - hand man in training the new generation of shinobi. His unique fighting style and determination could inspire the young ones and he could also be a great help in protecting the village during tough times.
A crossover with the Harry Potter world would be interesting. Naruto, as the Seventh Hokage, could visit Hogwarts. He might be confused by the magic there at first, but then start to find similarities between chakra and magic. He could even team up with Harry Potter to fight against a common enemy that threatens both the wizarding world and the ninja world.
Another possibility is Naruto traveling back to his own childhood days. He could mentor his younger self, teaching him advanced jutsu and wisdom he's gained over the years. This would make his younger self much stronger much earlier, and might also change how he interacts with Sasuke. For example, he could help his younger self better understand Sasuke's pain and prevent some of their earlier conflicts.
One common theme is legacy. Naruto has big shoes to fill as the Seventh Hokage, following in the footsteps of great leaders before him. Fanfictions often explore how he builds on their legacies and creates his own. Another theme is family. His role as a father and husband is important. We see how his family life impacts his decisions as Hokage. For example, he might make decisions to protect his family that also benefit the village.
It could be a rogue ninja who was once a part of the Akatsuki but managed to escape before their downfall. He's been biding his time, growing stronger, and now he wants to take revenge on Naruto and the Hidden Leaf for what happened to the Akatsuki.
Maybe in a crossover with the Bleach universe, Naruto as the Seventh Hokage discovers a strange spiritual energy leak that is affecting both the Soul Society and the ninja villages. He teams up with Ichigo to find the source of the leak and stop it. Along the way, they compare their powers and learn from each other.
One idea could be Naruto facing a new and mysterious threat from a hidden clan that has long been dormant. They could be trying to undermine the peace he has worked so hard to achieve as the Seventh Hokage.