These fanfics are appealing because they allow for a lot of creative interpretations. We can imagine how Naruto's jutsu and ninja skills would be perceived in Zuko's world. And how Naruto would handle the political and cultural aspects of Zuko's Fire Nation. The idea of Naruto helping Zuko also gives hope. It shows that even characters from different stories can come together and make a positive impact on each other's lives, which is a really heartwarming concept.
Well, there's a fanfic titled 'Naruto and Zuko: A Cross - World Bond'. In it, Naruto is somehow transported to Zuko's world. He then helps Zuko deal with his inner turmoil regarding his family and his place in the Fire Nation. Also, 'When Naruto Meets Zuko' is quite interesting. Naruto's ninja way of never giving up rubs off on Zuko, inspiring him to be more determined in his quest for redemption.
There's a fanfic titled 'Hinata's Comfort for Naruto'. In it, Naruto is heartbroken after a major loss in the village. Hinata, who has long admired him from afar, steps in. She first helps him by taking care of his daily needs like cleaning his messy apartment and doing his laundry. This simple act of kindness makes Naruto realize that someone truly cares. Then Hinata shares her own experiences of feeling alone and how she overcame it, which gives Naruto the strength to start anew.
One common way is by sharing its chakra. Naruto can draw on this extra chakra to increase his strength and speed. Another way is through its knowledge. Kyuubi has a long memory and can pass on useful information about the ninja world.
In these fanfics, Nagato may help Naruto on an ideological level. Nagato once believed in a very different way of achieving peace. By sharing his journey and how he came to realize the flaws in his thinking, he can guide Naruto in his pursuit of true peace. Nagato could also use his influence over the Akatsuki remnants to prevent them from causing more chaos, which in turn helps Naruto in his mission to protect the ninja world.
One possible reason could be the loss of a dear friend. Naruto values his friends deeply, and if he were to lose one, it would break his heart. For example, if Sasuke were to die or turn against him completely in a way that Naruto couldn't fix, it would be a huge blow.
For Naruto, he would further develop his understanding and compassion. He would see that even the most seemingly evil characters have a backstory and reasons for their actions. This would make him even more determined to save everyone he can. For Tobi, his development would be huge. He could go from a revenge - driven, shadowy figure to someone who realizes the error of his ways and wants to make things right. He might learn about the value of life and friendship from Naruto.
One possible plot development is that Nagato and Naruto form an alliance to take on a new, greater threat. This threat could be an ancient evil that requires both Nagato's power and Naruto's spirit. Another development could be Nagato using his abilities to help Naruto unlock new powers or forms. For example, he might help Naruto better understand the Sage of Six Paths' power within him.
One possibility could be that Sasuke, being the perceptive person he is, notices Hinata's unrequited feelings for Naruto. He might start by just being there for her, listening when she wants to talk about her feelings. They could go on training sessions together, and during those times, Sasuke shares his own experiences of dealing with complex emotions. This gradually helps Hinata to shift her focus from Naruto and start seeing herself as an individual with her own worth, rather than just someone pining for Naruto.