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.
It could be that his training in magic somehow awakens his haki. As he delves deeper into advanced magic spells and combat training at Hogwarts, his body and mind start to develop this new ability. For example, during a particularly intense dueling session, he feels a strange energy coursing through him which he later realizes is haki. His professors might initially be baffled by this new power, but as he learns to control it, it becomes an asset in his battles against the forces of evil.
Naruto's use of haki would be a game - changer for his combat skills. Haki has different forms. For example, the Observation Haki could allow Naruto to see the future movements of his opponents to some extent. This would combine really well with his already amazing combat skills like his Rasengan and Shadow Clone jutsu. He could use his clones more effectively to surround and attack his enemies while using haki to predict their counter - attacks.
Naruto would become more confident. With Conqueror's Haki, he would know he has an extremely powerful ability. This would boost his self - assurance in battles and in his leadership role. For instance, when leading his team, he would be more assertive.
One possible storyline could be Naruto discovers he has Conqueror's Haki during a battle with a powerful enemy. This new power gives him an edge and he uses it to inspire his allies and intimidate his foes. For example, when facing the Akatsuki, his Haki could make some of the weaker members hesitate in their attacks.
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 '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.
Maybe in the fanfiction, Naruto is the only one in the Ninja world who can use haki at first. This makes him an outcast and a target. But he uses his haki along with his ninja skills to prove himself and protect his village from threats that normal ninja techniques can't handle. He could also start teaching others about haki in the long run.
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.