A possible plot is that the Three - Tails Jinchuuriki discovers a unique ability related to the tailed beast that no one else knew about. For example, they could find a way to use the Three - Tails' chakra to heal others in a time of great need. This could also attract unwanted attention from those who would misuse this power. They then have to protect this new - found ability while also dealing with the normal challenges of being a Jinchuuriki.
Perhaps the Jinchuuriki is initially shunned by their village because of the dangerous power they hold. However, as the story progresses, they prove their worth by using the Three - Tails' power to defend the village from a powerful outside threat. This could lead to a journey of self - discovery and acceptance within the village, as well as new relationships being formed with the villagers who once feared them.
One interesting plot point could be the reaction of the other Jinchuuriki. Since Naruto now has the power of all the Tailed Beasts combined, the other former Jinchuuriki like Gaara might have mixed feelings. They could be both in awe of Naruto's new power and a bit envious at the same time.
Maybe a plot where a jinchuuriki loses control of their tailed - beast and the other jinchuuriki have to find a way to calm it down without harming their comrade. This could involve a lot of emotional moments as they try to reach out to the troubled jinchuuriki.
One idea could be exploring the relationship between the Jinchuuriki and Shukaku in more depth. Maybe the Jinchuuriki tries to communicate with Shukaku in a different way than in the original series, leading to new powers or understandings. Another plot could involve the Jinchuuriki being targeted by a new group who wants to use Shukaku's power for their own evil purposes. The Jinchuuriki then has to fight not only to protect themselves but also to keep Shukaku from being misused.
Well, you could focus on the relationship between the jinchuuriki and their extended family members in the fanfiction. For instance, how does the jinchuuriki's relationship with their grandparents change when they find out about the tailed beast? Also, a plot could revolve around the family trying to help the jinchuuriki control the power of the tailed beast. They could seek out ancient scrolls or wise sages to learn techniques that would make it easier for the jinchuuriki to co - exist with the beast.
One idea could be exploring the relationship between the 2 - Tails Jinchuriki and the other Jinchuriki in the Naruto world. Maybe they form an alliance to protect themselves from those who would use their power for evil.
In some fanfictions, characters like Jiraiya might be involved. He could be researching the Three - Tails Jinchuuriki phenomenon, trying to understand more about the connection between the host and the tailed beast. Tsunade could also make an appearance, especially if there are political aspects related to the Jinchuuriki in the story. For example, she might have to make decisions about how to protect the Jinchuuriki from outside threats while also ensuring the safety of the village.
One idea could be exploring the origin of the Ten - Tails in a different light. Maybe it was created by an ancient civilization for a noble purpose that got corrupted over time. Another could be a story where a young ninja discovers a hidden power within the Ten - Tails and has to learn to control it without being consumed by its dark energy.
Another possibility is that the time - traveling Ten - Tails Jinchuuriki ends up in a time during a great war. Their presence could either end the war quickly if they side with one of the parties, or make it even more chaotic as all sides would either try to recruit or eliminate this powerful being. They might also have the power to change the outcome of certain battles and thus reshape the world's power balance.
One plot idea could be Naruto struggling to control the 4 - tails form in a new and dangerous mission. Maybe he has to fight an enemy that specifically targets his unstable state. Another could be his friends trying different ways to help him calm down when he goes 4 - tails, leading to some heart - warming moments of friendship.
Perhaps in the fanfiction, the baby nine - tails gets separated from Naruto for a while. During this time, it has to fend for itself in a world that fears it. It could meet other friendly or hostile creatures and have various adventures before reuniting with Naruto.