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 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.
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.
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.
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.
In this fanfiction, perhaps Naruto's physical abilities are enhanced as the Kyuubi's kit. He might be able to move faster, jump higher, and his strength could be superhuman. Also, his relationship with Sasuke could change. Sasuke might see Naruto as an even greater threat or, on the other hand, an ally he needs to understand better. And Naruto could start to have a different understanding of his own identity and place in the ninja world.
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 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.
One idea could be exploring the relationship between Naruto and the Kyuubi no Kitsune in a more spiritual way. Maybe Naruto can have dreams where he actually communes with the fox spirit and gains new insights about his powers. Another plot could involve a situation where the Kyuubi's powers start to merge with Naruto in unexpected ways, causing him to develop new abilities that he has to learn to control quickly.
One idea could be that the female Kyuubi has the ability to transform into a human form and she becomes Naruto's secret protector. She uses her powers subtly to keep him out of harm's way while he's on his missions, and Naruto starts to notice strange things happening but doesn't know it's her at first.