It could be the First Hokage, Hashirama. Naruto would be amazed by his powerful Wood - Style jutsu and his ability to create the village. He could learn about the original ideals behind the Hidden Leaf from Hashirama.
Teamwork is also a big theme. Despite being the same person in essence, the two Narutos often have to learn to work together. This can be challenging as they may have different personalities due to their different experiences. For example, one Naruto might be more cautious while the other is more impulsive. And the theme of friendship also plays a role, as they are, in a way, their own best friends in these stories.
Well, it could be that Naruto meets the Hokage in a different time - space. They might work together to change some important events in the history of the village. For example, preventing a great disaster or changing the fate of some important characters. And Naruto could learn a great deal from the Hokage's wisdom and leadership in this encounter.
Well, 'Naruto meets Pain: The Alternate Ending' is a cool fanfic. In this story, Naruto uses a completely different strategy when facing Pain that we don't see in the original anime. It makes for a very exciting read. There's also 'Naruto and Pain: A Reconciliation' which explores what would happen if Naruto managed to convince Pain to change his ways much earlier in their encounter.
One possible fanfiction could be where Naruto discovers a dragon during one of his solo adventures. Maybe the dragon is injured and Naruto uses his kind heart and ninja skills to heal it. As he holds the dragon, he forms a special bond with it, and the dragon becomes his powerful ally in future battles against stronger foes.
It could be a majestic golden - scaled dragon that has been living in seclusion for centuries. Maybe it's a dragon that has the ability to control time, and Naruto's encounter with it is fated. The dragon might be female and is attracted to Naruto's strong will and determination.
Another plot could involve Female Naruto being a ninja from a hidden village that was thought to be extinct. She meets Naruto while on a mission to seek help. Naruto is intrigued by her and they end up going on a journey together to revive her village, facing many challenges and enemies on the way.
The World Government could be the main antagonist. They see both Luffy as a growing threat to their rule as a pirate and Dragon as a revolutionary. When Luffy and Dragon meet, the World Government might send their strongest agents like the Admirals to stop them from joining forces. The World Government's strict control over the world and their desire to maintain the status quo would put them in direct opposition to Luffy and Dragon.