You could also write a fanfiction where Naruto's oto has some sort of connection to his family history. Maybe it was something his father or mother was involved with, and Naruto has to learn about his past through the exploration of the oto.
Another idea is to create a story where Naruto discovers an ancient oto-related secret that has been hidden for generations. This could involve him going on a quest, meeting new characters who are also interested in the oto, and having to protect the secret from those who would misuse it.
A possible plot could be a time - travel story within the 'naruto kage oto fanfiction' world. The protagonist travels back in time and meets the previous generations of Kage. They then learn important lessons from them that they can use to change the future of the village. Or perhaps a story where different villages' Kage have to team up against a common enemy that is so powerful it requires their combined strength and knowledge.
One possible plot could be that the Kage of Oto has a secret alliance with Naruto. They work together to uncover a hidden threat to the ninja world that neither of their villages could face alone. This would involve a lot of intrigue, as they have to keep their alliance a secret from others who might not trust the Kage of Oto.
One of the potential allies could be Jiraiya. Even though he has his own ties to Konoha, he might see Naruto's leadership in Oto as a way to bring about a new balance in the ninja world. Also, some of the more open - minded members of Oto itself could become Naruto's allies. They might be impressed by Naruto's leadership skills and his vision for the organization, which could be different from what Orochimaru had in mind.
There could be an old and wise master in the Sound Village in this fanfic. This master has seen the village through many changes and has a deep understanding of the true power of sound. They could be mentoring a young protagonist, guiding them to unlock their potential related to sound - based abilities, and along the way, we could learn about the master's own past and how they came to be so knowledgeable about sound in the Naruto universe.
Naruto would face the challenge of resources. Orochimaru had his own ways of obtaining resources, some of which were unethical. Naruto would need to find legitimate ways to sustain Oto, whether it's through trade, alliances, or new forms of income generation. He also has to deal with potential threats from other ninja villages. They might see Naruto's leadership of Oto as a threat or an unknown variable and could take preemptive actions against Oto.
One interesting idea could be the combination of Naruto's ninja skills with mecha technology. For example, Naruto might use his chakra to power up the mecha in unique ways. Another idea could be the new enemies that are created specifically for this mecha - Naruto concept, like robotic shinobi that require different combat strategies compared to normal foes. Also, the design of the mecha Naruto itself can be really cool, perhaps with features inspired by the Nine - Tails.
One popular theme could be Naruto's inner struggle with his darker side. Another might be alternate storylines where Naruto's character takes a more morally ambiguous path. For example, a theme could explore how Naruto deals with power if it starts to corrupt him.
Another idea is that Aizen somehow ends up in the Naruto universe during the time of the Fourth Great Ninja War. He could try to manipulate both sides for his own gain. But Naruto, with his ability to see the good in people, might try to reason with Aizen and show him a different path. It could be a story of redemption or a great battle if Aizen refuses.
In a 'Naruto Mermaid Fanfiction', the mermaids could be in danger from an evil organization that wants to capture them for their precious scales. Naruto teams up with a mermaid princess to stop this threat and in the process, they learn about each other's worlds.
One idea could be a crossover where Naruto and Pucca end up in the same world due to a strange ninja jutsu gone wrong. Naruto is confused by Pucca's constant chasing of Garu, and he tries to help Garu escape in his own Naruto - style way.