One possible power from the devil gene could be the ability to resist certain types of genjutsu more effectively. Since the devil gene might be associated with a different type of energy or consciousness, it could disrupt the illusions created by genjutsu. Also, he could have an increased recovery rate. His body might be able to heal faster from injuries, almost as if the devil gene has a self - preservation aspect that accelerates the healing process.
He might gain enhanced physical strength. The devil gene could give him a boost in his taijutsu skills, allowing him to overpower opponents more easily.
If Naruto has the devil gene in fanfic, his powers might be enhanced in a different way compared to his normal chakra - based powers. He could gain abilities like the power to manipulate shadows in a more menacing way or have the ability to curse opponents. Also, his physical strength might increase but at the cost of some of his mental stability when using these powers.
He could probably gain the ability to phase through objects. Just like wraiths are often depicted as being able to pass through solid things. This would give him an edge in combat and also in sneaking around.
He could gain the power of controlling water like Poseidon's kids since he has good chakra control. It would be a new addition to his skill set.
Devil Naruto might possess the power of flight, which is common among devils in Highschool DxD. His chakra could be infused with devil energy, making his jutsus more powerful and having additional effects like draining the opponent's energy. His shadow clones could also be enhanced to have some devil - like characteristics, such as being able to resist certain types of attacks better.
One possible power is the ability to see through illusions more easily. Since the Kyuubi is a powerful entity, a doujutsu from it could give Naruto an edge against genjutsu users. It could break through complex illusions that would otherwise trap him.
Naruto could gain enhanced senses from the Ghost Rider powers. In the Naruto world, this would help him in detecting hidden enemies or traps more easily. The ability to ride the flaming motorcycle would also be a new skill. This could be used for quick transportation during missions or battles. He could also gain the power of transformation into the Ghost Rider form, which not only gives him a more intimidating look but also access to all the other Ghost Rider abilities. And with the Ghost Rider's connection to the spirit world, Naruto might be able to communicate with spirits in the Naruto universe, which could lead to new plot developments.
Well, Naruto could also gain some sort of enhanced perception. The Juubi has a connection to all things in the Naruto universe in a way. So, by holding it, Naruto might be able to sense things from much farther away, like threats or allies in need. This would give him a huge advantage in battles and also in his role as a protector of the village. He could react faster to any incoming danger.
He could gain the power of manipulation. Gaster might give Naruto the ability to manipulate space or time on a small scale. Maybe he could create small portals or slow down time for a short period during combat.
Perhaps he could have some sort of dark - based chakra manipulation. Demons usually have unique chakra, and Naruto's demon part might allow him to use a different form of chakra that gives him new jutsu, like the ability to create shadowy clones or dark - energy attacks.
He might gain a more powerful form of Rasengan, like a Rasengan that can change its shape and properties according to the situation. Maybe he has better control over his Nine - Tails chakra and can use it in more creative ways without losing control.