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.
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.
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.
An OC's Haki can be developed through intense training. Just like how Luffy and the others train in the One Piece world. They could face difficult opponents and learn from each battle, gradually strengthening their Haki. For example, if they constantly fight against Logia - type devil fruit users, their Armament Haki would improve to counter their intangible forms.
When Naruto uses blades in fanfic, his character can become more complex. He could be shown as more adaptable. For instance, if he starts using blades after losing his access to chakra for a while. This would force him to rely on a different form of combat, and his determination to still protect his friends and the village would shine through in his struggle to master blade - fighting. It could also show his creativity in combat, as he figures out ways to incorporate his existing skills with the new weapon.
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.
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.
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.
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.
Naruto's character could become more versatile. He'd have a new set of skills that require different thinking. Instead of just relying on ninjutsu and taijutsu, he'd have to understand the precision of Hokuto Shinken. This could make him more patient in battles.