It could be a new character created specifically for this fanfiction. Maybe a powerful wizard who has been in hiding and uses the mask to conceal his true appearance while he moves around Hogwarts or the wizarding world.
It might be related to a secret society or a dark magic object. In the Harry Potter universe, there are often mysterious items with special powers. The hollow mask could be one such item, perhaps used for disguises or to access hidden places.
One common theme could be power struggles. The black mask and hollow elements might bring in new and powerful abilities, leading to characters fighting over them or trying to control them.
The hollow mask could symbolize Naruto's hidden or repressed side. In fanfiction, it might represent a part of him that he keeps locked away, perhaps related to his past traumas or unacknowledged emotions.
In some fanfics, Naruto might be able to use a hollow mask through some creative plot devices. Maybe it could be due to some sort of cross - over magic or a unique power - up he receives. However, this is completely a product of fanfiction and not part of the original Naruto lore.
It would be really cool. He might look really intimidating with the hollow mask on. And his fighting style could change completely, incorporating some elements from the concept of hollow masks, like maybe some dark - energy - based attacks.
Well, if Naruto got a hollow mask in fanfiction, he might gain new powers. The hollow mask could potentially enhance his speed and strength, like how it did for characters in Bleach. He could also use it to intimidate his enemies. Maybe it would give him a new form of chakra or a special jutsu that combines his ninja skills with the power of the hollow mask.