Well, Naruto might face environmental challenges. For example, if the toddler is in a swampy area or a place with a lot of quicksand. Naruto has to navigate through these difficult terrains while protecting the toddler. Also, if there are other threats around like poisonous plants or insects, he has to be aware of them too. He can't just focus on getting the toddler out, but also has to ensure their safety during the whole process. This requires his full attention and all his ninja knowledge.
The Kumo ninjas could also be working in a coordinated way. They might have a strategy to isolate Naruto and keep him away from Hinata. Naruto has to break through their formation. And if the Kumo ninjas have some sort of intel on Naruto's abilities, they could plan their attacks accordingly. So Naruto has to be constantly on his toes and come up with new tactics to overcome these challenges and save Hinata.
One challenge could be getting the necessary resources. Uzushiogakure was destroyed long ago, so finding materials to build the village again would be tough. He might have to negotiate with other villages for supplies.
Another problem might be the lack of proper resources. Even if Naruto has the ability to heal, he may not have all the necessary herbs or medical equipment. In the world of Naruto, some healing requires specific items. If they are in a remote location or in a battle - torn area, getting these resources could be a huge hurdle.
One challenge could be facing powerful new enemies. In fanfiction, authors often create unique and formidable foes for Naruto. These enemies might have strange powers or abilities that Naruto has never encountered before, forcing him to quickly adapt his fighting style. Another challenge could be the moral dilemmas. He might have to make tough decisions in the chaos of war, like whether to sacrifice a few to save many.
One challenge could be that the heartless have a very different nature compared to the beings Naruto is used to dealing with. Their lack of emotions might make it difficult for him to find a way to connect and control them.
One common theme could be heroism. Naruto is known for being a hero, and in these fanfics, he shows his heroic side by saving the toddler. Another theme might be protection, as he safeguards the young and vulnerable toddler.
Chakra depletion is also a big issue. With all the chakra - control exercises and sparring, Naruto could run out of chakra quickly. This would not only limit his ability to practice jutsu but also leave him vulnerable in case of an unexpected attack during training.
In the fanfiction, another challenge Naruto might face is dealing with any mind - control or brainwashing techniques the enemy may have used on Ino and her squad. If they are turned against Naruto, it becomes a more complicated situation. He not only has to free them from the physical danger but also has to break the mind - control. And if the enemy has allies that keep coming, Naruto will have to fight continuously while also protecting Ino and her squad, which requires a great deal of stamina and strategic thinking.
One challenge could be the difference in their natures. Madara is an Uchiha with a more cold and calculating style, while Naruto is more impulsive and emotional. Adjusting to Madara's training methods which are likely to be strict and demanding could be tough for Naruto.
One challenge could be the strength of the Kumo ninjas. They are known for being tough. Naruto might have to face some powerful jutsu from them. Another challenge could be the distance. If Kushina is held deep in Kumo territory, it would be hard for Naruto to reach her without being detected.