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 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.
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.
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.
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.
One possible plot could be that Naruto discovers the Chidori technique while training in a secret area. Maybe he stumbles upon some old scrolls left by Kakashi. He then has to train hard to master it, facing difficulties like controlling the lightning chakra. As he progresses, he combines it with his own unique Rasengan, creating a new and powerful jutsu.
One possible plot could be that Naruto discovers an ancient scroll that has a simplified version of the Rasengan technique. He spends days secretly practicing it in the forest, facing initial failures but gradually getting the hang of it. With his new - found skill, he surprises his friends and even manages to use it in a sparring match against Sasuke, changing the dynamics of their rivalry early on.