Another challenge could be dealing with the interference of enemies. As Naruto is trying to create powerful weapons, his enemies would not want him to succeed. So they might try to steal the materials he has collected or attack him while he is in the middle of forging, forcing him to defend himself and his work at the same time.
Naruto could struggle with the technical skills needed for forging. Even with his determination, learning the precise techniques to shape and temper the weapons to his liking could be difficult. He might need to find an expert to teach him or learn from ancient scrolls.
In this fanfiction, Naruto might also create a shield. This shield could be made from a combination of rare materials he discovers during his adventures. It has the ability to not only block physical attacks but also absorb and redirect chakra - based attacks back at the enemy.
In fanfiction, Naruto may face challenges related to politics. Other villages may see the restoration of the Uzumaki clan as a threat to the balance of power. They could try to interfere in Naruto's efforts through various means such as spreading false rumors about the Uzumaki or even sending spies or assassins. Additionally, Naruto has his own duties as Hokage, so he would need to balance his time between running the village and restoring his clan.
One challenge could be finding enough Uzumaki descendants. Since the clan has been through so much, there may be very few left. Another might be dealing with the political implications. Other clans might be jealous or fearful of a resurgent Uzumaki clan.
In the fanfiction, Kakashi might face the challenge of Naruto's insecurities. Naruto has always had a complex about being alone and not having a family. Kakashi would have to find ways to make Naruto feel secure and loved. Also, dealing with Naruto's powerful and sometimes uncontrollable chakra could be a problem. Kakashi would need to train Naruto to master his chakra properly without it overwhelming him.
One challenge could be controlling the space - time aspect of Kamui. It's a very complex jutsu, and Naruto, who is used to more straightforward chakra - based attacks, might struggle to understand the intricacies of warping space and time.
Financial difficulties could also be a problem. Naruto might not be well - off initially, and raising a child requires money for things like food, clothes, and education. He would have to find ways to provide for his sister while still being a ninja. Also, there could be threats from Naruto's enemies who might try to target his sister to get to him.
One challenge could be the physical differences in his body compared to those who traditionally learn the Black Leg Style. Naruto's own ninja training has focused on different aspects like chakra control for his shadow clones, and adjusting to the more physical and acrobatic demands of the Black Leg Style might be tough.
Also, he may face opposition from others in the village. Some might think that Naruto is straying from his traditional ninja path by learning a sword style. They could try to discourage him or not support his training, which would be an additional hurdle for him to overcome as he tries to master this new skill.
One big challenge would be getting recognition from other villages. They might see his new village as a threat or not take it seriously at first. Naruto would have to prove that his village is a legitimate and peaceful addition to the ninja world.
One challenge could be the complexity of the jutsu itself. His father's jutsu might be very advanced and require a high level of chakra control that Naruto doesn't initially have.