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.
For Naruto, he may gain a new perspective on power. Instead of just seeing the Kyuubi as a source of brute strength, he could start to understand the deeper, more complex nature of the tailed beast. This could lead to a more mature Naruto, one who is not just about fighting but also about protecting through a more nuanced use of power. The male Kyuubi could experience a change in his view of humans. He might see that not all humans are out to control or harm him, especially with Naruto as his'mate'. He could become more empathetic towards the human world and be more willing to cooperate with Naruto's goals.
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.
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.
In the Naruto fanfiction with Naruto having Hashirama's chakra, there are several potential plot developments. Firstly, Naruto could use the chakra to revive some of Hashirama's old techniques and use them to fight against a new, powerful enemy. This would involve a lot of training and exploration of Hashirama's memories that might be stored within the chakra. Secondly, the chakra could attract the attention of ancient entities or clans that were once associated with Hashirama. They could either help or hinder Naruto depending on their motives. Thirdly, Naruto might have to deal with the psychological impact of having such a powerful and different type of chakra. This could lead to internal struggles as he tries to balance his own identity with the new power he has acquired.
One plot development could be that Naruto discovers an underwater world full of secrets and new enemies. He might have to use his new ability to navigate this world and uncover the mysteries there.
A potential plot development could be that Kushina helps Naruto master his nine - tails chakra much sooner. She has a connection to the nine - tails as its former jinchuriki, so she could teach Naruto how to better coexist with it and use its power more effectively.
One potential plot development could be that Naruto has to face new, more powerful enemies who are drawn to his newfound power. Another could be that he has to learn to control the combined power of all 9 bijuu, which might be a difficult and dangerous process.
A potential plot twist could be that the arranged marriage was actually a ruse set up by an enemy. They might be planning to use the opportunity of the marriage to get closer to Naruto and somehow steal the Kyuubi's power.
Another plot development could be that Naruto's Asura's power reveals a hidden history or prophecy. This could send him on a quest to discover more about his power's origin and what it truly means for the future of his world. Along the way, he would meet new characters, both friend and foe, and face various challenges that test not only his power but also his beliefs and values.
Another plot development could be the impact on the other characters in the Naruto universe. The presence of a fem Kyuubi might change how characters like Sasuke view Naruto. They could be more intrigued or even more hostile depending on how they perceive the new relationship between Naruto and the fem Kyuubi. Also, the village elders might react differently, perhaps with more fear or more acceptance, which would then influence the overall political and social situation in the village.