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.
Percy often uses Observation Haki to anticipate the attacks of his enemies. He can sense their movements and intentions, which gives him an edge in combat, especially against fast - moving or sneaky foes like some of the monsters in the Percy Jackson world.
The chapter where Yun Qianyue opened the Phoenix Tribulation in the hedonistic princess consort was called " Heavenly Domain ". This novel was a fantasy novel about the love story between a young noble who had the power of God and an ordinary girl. In the novel, Yun Qianyue activated the Phoenix Tribulation and experienced a series of tests and challenges before finally becoming a powerful god.
Haki can completely shift the power dynamics. If a character like Ron suddenly discovers Haki, he could become a much more formidable opponent. He might be able to use it to intimidate Death Eaters or other dark wizards, adding an edge to his character that wasn't there before.
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.
I'm not sure specifically what that particular 'ash unlocks aura fanfiction' is about without reading it. It could be about a character named Ash who somehow unlocks an aura in a fictional story, perhaps in a world of magic or superpowers.