Another possibility is that the main antagonist is a group of power - hungry individuals who want to take Naruto's control of the Nine - Tails for themselves. They could be from within Konoha or from other villages. They might try to manipulate Naruto, or if that fails, they'll try to steal the Nine - Tails' power by force. They would likely be very skilled and have some devious plans up their sleeves.
One possible plot development could be that Naruto uses his new - found control of the Nine - Tails to defeat a powerful enemy that was previously unbeatable. He might be able to combine his own ninja skills with the Nine - Tails' power in a more efficient way, like creating new and unique jutsu.
Naruto's friends could also be of great help. Sasuke, despite their complex relationship, might have some knowledge or abilities that could contribute. Sakura, with her medical skills and her growth as a ninja, could support Naruto in his training. And even his other friends like Shikamaru, who is known for his intelligence, could come up with strategies for Naruto to better approach the task of controlling the Nine - Tails. The entire Konoha village in a way could also be seen as a helper, as it provides the environment and resources for Naruto's growth.
In some fanfictions, Naruto achieves complete control of the Nine - Tails through intense mental training. He might enter a special mental space where he has to face the Nine - Tails directly and prove his worthiness. By showing unwavering determination and a deep understanding of the power, he slowly gains the upper hand.
In this fanfiction, Naruto probably has to first learn about the nature of the Nine - Tails' power. He may start by exploring his own family history related to the Nine - Tails. Then, he could encounter some challenges like the Nine - Tails' resistance to being controlled. But Naruto, with his determination, might find a way to communicate with it. For example, he could enter his mind - scape and have a direct conversation with the Nine - Tails. This could be a major turning point in his journey to control it.
The consequences for Konoha's economy would also be significant. Rebuilding all the damaged infrastructure would cost a great deal of money. The trade within the village might be disrupted as well, since many of the shops and markets could be destroyed. Also, the ninja academy might have to be closed temporarily if it's damaged, which would affect the future generation of shinobi in Konoha.
The Hokage, depending on who it is at the time. They are usually very powerful shinobi. For example, if it's Kakashi, he could use his Sharingan and his vast array of jutsu to try and stop Naruto. He has experience dealing with powerful opponents and might be able to come up with a strategy to calm Naruto down or at least restrain him.
Maybe through new jutsu or abilities. The fanfiction could give Naruto some unique power that allows him to communicate or negotiate with the Nine - Tails on a different level. He could use this power to show the Nine - Tails a different perspective, like the potential for harmony between them instead of constant struggle.
Yes, in some fanfictions, Naruto is often depicted as having a very special connection to the Nine - Tails that goes beyond the normal relationship in the original story. For example, he might be able to fully control the Nine - Tails' power in ways not shown in the canon, or they could have a mental bond that allows for unique forms of communication and cooperation.
One popular plot is Naruto using the Kyuubi's power to protect Konoha from a new, powerful enemy. For example, he might face off against a group of rogue ninja who have united to take over the Hidden Leaf. Another plot could be Naruto exploring the memories of the Kyuubi, which leads to him learning ancient ninja secrets. This could involve finding lost jutsu or understanding the history of the ninja world better. Also, some fanfictions might have Naruto using the Kyuubi's power to finally bring peace between the ninja villages by showing his overwhelming strength and his will for peace.