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.
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.
Yes, there is a Ninja Kamui manga. It has gained popularity for its action-packed scenes and interesting character developments. Many fans enjoy collecting and reading it.
In a fanfic where Naruto knows the Chidori, it could change the power dynamics in battles significantly. Naruto's already vast chakra reserves combined with the piercing and fast - acting nature of the Chidori would make him an even more formidable opponent. He could use it in close - quarter combat situations, perhaps integrating it with his Shadow Clone Jutsu in creative ways. For example, he could have clones perform the Chidori from different angles, catching his enemies off - guard.
Naruto using Kamui could change the power dynamics in the Naruto universe in the fanfiction. His battles would become more unpredictable. For instance, against strong opponents like Madara or Kaguya, Kamui could be used in creative ways. He could use it to send parts of their attacks to another dimension, or quickly dodge attacks and counter - attack from unexpected angles. It also might make his allies view him differently, as this new power is something very different from his normal ninjutsu.
In many fanfictions, Naruto might initially discover Kamui through an encounter with Obito or Kakashi. Maybe during a battle where he witnesses the power of Kamui first - hand, and his inquisitive nature leads him to start exploring how to learn it.