One interesting plot could be Naruto fully transforming into the Nine - Tailed Fox during a battle against a powerful enemy. His friends are initially shocked but then try to find a way to bring him back to his senses.
One possible plot twist could be that Naruto loses control over his transformation into the Nine - Tailed Fox in a completely unexpected situation. Maybe during a friendly spar with his friends, and this causes them to fear him in a new way. It would add a whole new layer of drama to their relationships.
His relationship with the villagers could become more complex. Some might see him as a greater threat, while others who have come to know Naruto as a hero might be more accepting. His transformation could also lead to new alliances as some might want to use his power for their own purposes, which Naruto would have to navigate carefully to protect his relationships.
Obviously Naruto himself, as he is the one turning into the Nine - Tailed Fox. Sasuke would also likely be involved. He might be the one to try and reach Naruto when he is in his fox - form, either to fight him or to bring him back. Sakura too, she could use her medical ninjutsu to try and help Naruto if he gets injured during the transformation.
In this type of fanfiction, often Naruto's transformation into the nine - tailed fox can lead to some really cool battle scenes. He could use the fox's speed and strength in unique ways. Like, he might be able to run up walls or jump extremely high to attack enemies from unexpected angles. Also, there could be a plot where Naruto has to enter a sort of spiritual realm within himself to communicate with the nine - tailed fox and gain better control over their combined form.
It could make his friends more cautious around him. For example, Sakura might be a bit more hesitant to get close, fearing the power of the Nine - Tailed Fox. But at the same time, some like Sasuke might see it as an opportunity to become stronger by sparring with Naruto in this new form.
There are fanfictions where the Nine - Tailed Fox has a split personality. One side is the fierce and powerful beast, and the other is a more gentle and understanding entity. Naruto has to deal with both sides, which creates a very complex and different kind of relationship compared to the original series. This can lead to some really interesting character development for Naruto as he tries to balance and understand this unique relationship.
He also has to deal with the public perception. People who are afraid of the nine - tailed fox might start to shun or even attack Naruto. And in battles, his enemies might target his connection to the nine - tailed fox, trying to force him to transform and lose control. He needs to be constantly vigilant about this.
In fanfiction, when Naruto unleashes the Nine - Tailed Fox, it often leads to intense and action - packed scenes. Writers might explore the raw power Naruto gains, how it affects his relationships with friends like Sasuke and Sakura. For example, they could be in awe or even a bit scared of this new, more powerful Naruto.
In RWBY fanfiction, the concept of Naruto's Nine - Tailed Fox could be really interesting. One way it could be incorporated is by having a character in the RWBY universe inherit the power of the Nine - Tailed Fox somehow. Maybe a Grimm could be created that has similar characteristics to the Nine - Tailed Fox, like its powerful chakra - like energy. This would add a whole new level of danger and mystery to the RWBY world.