There are many possibilities. It could be that a new character, a powerful but reclusive ninja, decides to teach Naruto both the Chidori and the Rasengan. This new character might see Naruto's potential and believe that these two jutsus in Naruto's arsenal would change the course of future battles. Another option could be that Naruto discovers some ancient scrolls that detail the techniques of both jutsus and through his own study and practice, he learns them, without a traditional teacher.
Maybe Sasuke teaches him the Chidori in a moment of camaraderie. And for the Rasengan, it could be an older and wiser Naruto from the future who travels back in time to teach his younger self.
It could be Kakashi. Since he's already Naruto's teacher and he knows both techniques. He could guide Naruto in understanding the intricacies of the Chidori, like how to form the lightning - chakra in his hand, and for the Rasengan, he could give more advanced tips on chakra control.
In a fanfiction like this, the plot might involve Naruto struggling to master both techniques. He could start by observing Sasuke use the Chidori and then try to incorporate its lightning - based power into his own jutsu. For the Rasengan, he might have new insights while training, perhaps finding a way to combine it with the Chidori for an even more powerful attack. Along the way, he would face challenges like controlling the chakra flow for both techniques and dealing with opponents who are also after these powerful jutsus.
Well, he might start with intense training sessions. Maybe he observes Kakashi closely for the Chidori, and for the Rasengan, he practices over and over again, gradually getting the hang of the chakra control required.
In many Naruto fanfictions, the Chidori - Rasengan combo is often portrayed as an extremely powerful and unique move. It combines the piercing nature of the Chidori with the rotational and explosive force of the Rasengan. Some fanfictions might have Naruto or Sasuke (or both in some cases) creating this combo during a crucial battle against a powerful enemy, like a new Akatsuki member or a rogue ninja from another village. This combo is usually described in great detail, with the lightning - chakra of the Chidori surrounding and enhancing the Rasengan, making it not only more destructive but also having an added effect like paralysis due to the electricity.
In a more creative fanfic, an ancient ninja who was the originator of the Chidori technique could appear. This ninja could be brought back to life through some sort of magic or jutsu. He sees Naruto's pure heart and decides to pass on the Chidori knowledge to him, believing Naruto will use it for good.
One creative way is to give it different elemental properties. Instead of just the basic lightning and wind/rotational aspects, they might add fire or water elements to it. For example, if there's a situation where they need to fight an ice - using enemy, they could add fire to the combo to melt the ice. Another way is to have it used in a non - combat way. Maybe Naruto and Sasuke use it to break through a powerful barrier that's not just physical but also has some sort of chakra - based lock on it.
The Naruto learns Rasengan fanfic can take the story in various directions. One direction could be a more in - depth exploration of the Rasengan's origin within the context of the fanfic. Another could be a time - travel plot where Naruto goes back in time and teaches his younger self how to learn Rasengan faster. It might also focus on the emotional turmoil Naruto goes through when he struggles to learn the jutsu, especially if he feels like he's letting down his village or his teacher Jiraiya.
In some fanfictions, Kakashi could also play a role. He is very knowledgeable and has seen the Rasengan in action. He might offer some tips on chakra control, which is crucial for Naruto to master the Rasengan.
One factor that makes a 'Naruto Learns Rasengan Fanfic' great is the ability to add new elements to the story. Instead of just repeating what happened in the anime or manga, it could introduce new challenges for Naruto. Maybe there's a new enemy who is also after the Rasengan's secrets, and Naruto has to learn it quickly to defend against them. Additionally, the fanfic should have a good pacing. It shouldn't rush through Naruto's learning process but also shouldn't drag it out too long.
Sasuke could be Naruto's teacher. Since Sasuke is a master of the Chidori, he might decide to teach Naruto as a way to make Naruto a more formidable ally. They have a complex relationship, and this could be a way to strengthen their bond.