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.
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 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.
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.
One challenge could be the chakra consumption. Shadow travel might require a large amount of chakra, and Naruto has to learn how to manage it. If he uses it too often or for long distances, he could run out of chakra in the middle of a mission or a fight.
One challenge could be the cultural differences. Naruto is from a ninja world, and the lycans have their own unique culture. Understanding and respecting those differences while still leading effectively can be tough.
One challenge could be that the enemy is too powerful for Naruto to defeat on his own. He might have to quickly level up his skills or find allies to help him. For instance, he might need to convince some of the more reluctant ninja in the village to join him in the fight.
One challenge could be controlling it. Haki is a different kind of power compared to chakra, so Naruto would have to learn how to regulate the flow and intensity of his haki. For example, if he uses too much haki at once, it might drain him quickly.
He also has to deal with the public perception. People who are afraid of the nine - tailed fox might start to shun or even attack Naruto. And in battles, his enemies might target his connection to the nine - tailed fox, trying to force him to transform and lose control. He needs to be constantly vigilant about this.