Maybe an ancient sage in Naruto's own world who has long - been in seclusion. This sage has knowledge of different power systems beyond just chakra. He notices Naruto's pure heart and strong will and decides to pass on his knowledge of haki to Naruto, believing that Naruto can use it for the greater good of the ninja world.
It could be an alien being who crash - lands in the Naruto world. This alien has a unique form of energy similar to haki. Recognizing Naruto's power and his thirst for knowledge, the alien decides to teach Naruto about haki - like abilities. Naruto, with his open - mindedness, quickly grasps the concepts and starts to develop his own haki - based powers.
Well, in such a fanfic, Naruto could start learning haki perhaps from a mysterious traveler who has knowledge of different worlds. He might first struggle with understanding the concept of haki, like differentiating between Observation Haki and Armament Haki. Then, as he trains, he could gradually incorporate haki into his existing jutsu. For example, using Armament Haki to strengthen his Rasengan, making it even more powerful and capable of breaking through tough defenses that normal Rasengan couldn't. This would make him an even more formidable opponent in battles against tough enemies like Madara or Kaguya.
In some fanfictions, Naruto might discover haki during a particularly intense battle. Maybe when facing an enemy with an unusual power that his regular jutsu can't handle, he unknowingly taps into his latent haki ability.
In 'naruto haki fanfic', Haki can change the Naruto universe by adding a new layer of power. For example, it can make battles more complex as characters now have to consider both chakra and Haki. It might also change the way characters interact with each other, as those with Haki could sense things differently.
In a fanfic where Naruto uses haki, it could change his relationships with other characters too. For example, if he shows this new power, some characters might be in awe of him, while others might be jealous. His training to master haki could also lead to new interactions with mentors or allies who are familiar with this power. Also, his use of haki could potentially attract the attention of new enemies who are interested in this unique ability.
I think Conqueror's Haki would suit Naruto. He has that natural leadership and strong will, just like characters in One Piece who possess Conqueror's Haki. It would be a great addition to his existing confident and determined personality.
Dumbledore could be the one to teach Harry about Haki. Dumbledore, with his vast knowledge of magic and the unknown, might have come across Haki in his travels. He could recognize the signs of Haki in Harry and take it upon himself to guide Harry in understanding and controlling this new power. He would use his calm and wise approach, just like when he teaches Harry about other aspects of magic.
Perhaps Naruto discovered a hidden power within himself that was similar to Busoshoku Haki. In the fanfic, the author might have created a new backstory for Naruto where his Uzumaki heritage had some latent abilities that could be manifested as Haki - like powers. So, he just had to figure out how to use it on his swords.
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.
In this fanfiction, Naruto's development with Haki could be quite interesting. Firstly, Haki could enhance his sensory abilities even more than his regular chakra - based perception. This would allow him to detect threats from afar and better protect his village. His physical attacks could also become more powerful. He might start to train with different characters who are more familiar with Haki, like if there are any characters from other universes introduced. This could lead to him learning new values and cultures, expanding his world view, which in turn would shape his character in a more complex and mature way.
Yes, in many Naruto fanfictions, authors often give Naruto the power of Haki. It's a creative way to blend the concepts from One Piece (where Haki exists) with the Naruto universe. This can lead to really interesting storylines, like Naruto using Haki to sense enemies' intentions better during battles or using it to enhance his existing jutsu.