It could be a powerful and mysterious shinobi. Maybe someone from an ancient hidden village who has been observing Naruto for a long time and decided to give him the mask as a test or a way to unlock his true potential.
Perhaps it was given to him by a spirit. In the world of Naruto, there are many spirits and entities. A spirit that has a connection to the concept of the hollow mask might have bestowed it upon Naruto. This spirit could have its own motives, like using Naruto as a vessel to carry out some sort of plan in the ninja world.
It's possible that Naruto found the hollow mask himself in some long - forgotten ruins. The ruins could be from an era long past, and the mask was left there by an unknown force. Naruto, being his curious self, put on the mask and then had to deal with the consequences and powers that came with it.
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.
Maybe it was Jiraiya. Jiraiya was a very important figure in Naruto's life. He could have given Naruto the mask as part of a training exercise. He might have thought that wearing a mask would force Naruto to rely more on his intelligence rather than his brute strength in certain situations.
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.
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.
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.
Iruka sensei could have given it to him. As Naruto's first teacher and someone who has always supported him, it would be a great way to show his pride in Naruto's growth as a ninja.
In the 'naruto has a mask fanfiction', it might be that Naruto finds the mask himself. He could stumble upon it during one of his adventures, perhaps in an ancient ruin or a hidden cave. The mask could be enchanted or have some special property that draws Naruto to it, and he decides to keep it and figure out its secrets on his own.
The mask in the 'naruto has a mask fanfiction' might be a symbol of mystery. It could hide Naruto's true identity or feelings. Maybe he uses it to conceal a new power he has acquired and doesn't want his enemies to know about right away.
It could be Orochimaru. He's always interested in powerful artifacts, and the mask Naruto gets would be no exception. Orochimaru would likely try to steal the mask from Naruto to add to his collection of powerful items and use its power for his own dark experiments.
In such fanfiction, Naruto's personality could be a mix of his old self and a new, more complex version. He would still be the determined and kind - hearted Naruto at heart. However, the power of the hollow mask might make him more secretive. He might keep things from his friends and mentors for fear of them trying to take the mask away. This internal conflict between his old and new self could be a major part of his character development.