Often, his enhanced hearing could be depicted as being able to pick up on whispered spells from a distance. It might be described as an extension of his natural magical abilities. Maybe he can sense danger approaching through a tingling in his senses, like a premonition but more acute due to his enhanced senses.
In some fanfictions, there could be new characters introduced specifically for the plot related to Harry's enhanced senses. For instance, a wise old wizard who has knowledge about this rare magical phenomenon and guides Harry through it. There might also be antagonists who are either threatened by Harry's new powers or are trying to use them for their own evil purposes.
He might become a target. If there are villains in the X - Men universe who don't want someone with such powerful senses around, they could try to take him out. His enhanced senses could also make him a bit of an outcast among normal humans in the fanfiction world, as they might not understand his abilities.
One challenge could be sensory overload. With enhanced senses, there would be so much more information coming in. For example, in a crowded Hogwarts corridor, he might be bombarded with all kinds of smells, emotions, and sounds. This could be overwhelming and make it difficult for him to focus on important things like his studies or a mission.
Well, it could make his interactions more intense. For example, if he's interacting with Hermione, he might be able to sense her emotions more acutely. He could tell when she's frustrated or excited even before she shows it clearly. This could lead to him being more empathetic towards her, or it could cause some misunderstandings if he misinterprets what he senses.
In the X - Men fanfiction, Harry Potter's enhanced senses could be a new factor in mutant - human relations. His ability to sense things differently might make mutants see humans in a new light. Maybe he could sense the emotions of mutants more acutely, which could lead to better understanding between the two groups. Also, his enhanced senses could be used in training new X - Men recruits. He could detect their potential and areas of improvement more accurately than normal humans.
In some fanfictions, Naruto's enhanced hearing allows him to eavesdrop on important conversations from a great distance. This gives him an edge in the political intrigue within the ninja villages. For instance, he overhears a plot against a village leader and is able to stop it in time. It adds a new layer of depth to his character and the overall plot of the fanfiction.
They can be used to solve mysteries. His sense of smell could detect a unique odor left by a missing person or a clue at a crime scene. His enhanced hearing might pick up on a whispered password or a hidden message in a seemingly normal conversation.
In enhanced Harry Potter fanfiction, the settings often play a major role. Authors might expand on the wizarding world, like describing more about the other wizarding schools around the world. Plot twists are also common. For instance, there could be a different outcome to the Triwizard Tournament. And, of course, the use of magic can be more elaborate, with new ways of using existing spells or creating entirely new ones.
Well, it could be a fanfiction that combines different elements of the Harry Potter universe in a more elaborate or enhanced way. Maybe it takes various storylines from the original books and movies and splices them together to create a new and unique narrative.