One interesting plot development could be Naruto using Kyuubi's power in a new and unexpected way in a battle. For example, he might be able to combine it with his Rasengan in a more powerful form that no one has ever seen before. This could give him an edge against a really strong enemy.
One idea could be that the power transfer is not straightforward. Maybe Kyuubi's power starts to change Naruto's appearance in unexpected ways, like giving him fox - like features that he has to learn to hide. This could lead to some comical and also tense moments as he tries to keep it a secret from his friends.
One possible plot development could be Naruto gaining new and extremely powerful abilities. For example, he might be able to use Kyuubi's chakra in more refined ways, like creating unique jutsu that combine his own skills with the raw power of the Kyuubi. This could make him nearly invincible in battles against his enemies. Another aspect could be his relationship with his friends and the village. With the new power, some might fear him while others try to understand and support him. It could also lead to Naruto having to face new and stronger foes who are attracted by his enhanced power.
Maybe Naruto gains new insights into the nature of chakra. The Kyuubi's chakra is very different from his own, and through the merge, he could understand how to manipulate chakra in ways he hadn't considered. This could lead to him teaching others new ways of using chakra as well.
One exciting plot development could be the discovery of a new, hidden jutsu that gives Naruto an unexpected power boost. For example, he might find a scroll left by an ancient sage that contains the knowledge of a super - powerful space - time ninjutsu. This new jutsu could help him in battles against extremely strong foes like Kaguya.
In some 'naruto is banished fanfic', one interesting plot could be Naruto finding a new hidden village that accepts him wholeheartedly. He might then train with unique jutsus there and form new alliances.
One interesting plot idea could be exploring how Minato's relationship with the Kyuubi affects Naruto. For example, Naruto discovers some hidden memories of Minato's encounter with the Kyuubi that give him new powers or insights. Another idea is a story where Minato has to return from the afterlife briefly to help Naruto control the Kyuubi's power more effectively. Maybe there could also be a plot where the Kyuubi has a change of heart due to Naruto's kindness and decides to reveal secrets about Minato that no one else knew.
On the other hand, it could also strengthen his relationships with some characters. For instance, Kakashi, as his teacher, could be more proud of Naruto's growth in harnessing such a powerful force. And Naruto might also become a more respected figure among the younger ninja, who look up to him for his new - found power.
A possible plot development might involve Naruto exploring his own past to understand how he became the Kyuubi's father. He could discover secrets about his own family or ancient jutsu that led to this situation. Along the way, he might face opposition from those who don't want this relationship to be known or who fear the implications it could have on the balance of power in the ninja world. This would lead to many conflicts and challenges for Naruto to overcome in the fanfiction.
Well, a cool plot might be that Naruto uses the Nine - Tails to travel to different dimensions. He could explore places that were previously unknown and discover new powers or allies there. Also, in the fanfic, he could use the Nine - Tails' chakra to heal the land that was damaged by previous battles. This would show his growth not just as a fighter but also as a protector of the village and its surroundings.
Perhaps Naruto's relationship with the other villagers changes more rapidly. In the original story, they were initially afraid of him because of Kurama. But with all of Kurama sealed in him from the start, they might be more in awe or more fearful, which could lead to different interactions. He might also have a different standing among the ninja in his village, being seen as a more immediate and powerful asset or threat, depending on how they view the power of Kurama.