In this type of fanfiction, an interesting concept could be the enhancement of a character's body to withstand extreme magical conditions. For instance, being able to survive in the Forbidden Forest without any protective spells due to an enhanced immune system against dark creatures. This could change the way the characters interact with the dangerous parts of the wizarding world. They could explore areas that were previously too dangerous and uncover secrets that were hidden there.
Definitely, Neville Longbottom is a character that shows up often in such fanfictions. He might have an enhanced body that gives him a newfound confidence. Maybe his body is enhanced to be more in tune with herbology, like being able to communicate with plants on a deeper level. Ginny Weasley is also a popular choice. She could have an enhanced body that makes her a more powerful witch, with the ability to perform complex jinxes and hexes with ease, and also be more agile in battles.
The Devil Gene could be integrated as a new form of magic that has been hidden for centuries. A character might discover it accidentally and start to explore its powers, which could lead to new adventures and challenges.
Well, perhaps in this fanfiction, the devil gene is awakened when Harry is exposed to a powerful and cursed object. As the gene awakens, he starts to have strange visions and an uncontrollable urge for power. His Hogwarts experience completely changes as he has to deal with this new aspect of himself. He may also attract the attention of dark forces that want to use his newfound power for their own evil purposes.
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.
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.
Another concept could be a conflict between those with the Devil Gene and the traditional wizarding society. The Devil Gene might be seen as something dark and dangerous, so there could be a lot of prejudice and attempts to control or eliminate those who possess it. This could create a really tense and interesting story dynamic.
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.
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.