Definitely Naruto himself. Since it's a Naruto face mask fanfic, he should be the central character. His friends like Sasuke and Sakura can also be included. Sasuke could be jealous of the attention Naruto's mask gets, or Sakura could be the one to patch up the mask when it gets torn in a battle.
One idea could be a fanfic where Naruto's face mask becomes a magical item. Maybe it has the power to hide his presence completely from enemies, leading to some really cool stealth missions.
One possible reason could be for disguise. Maybe he is on a secret mission and doesn't want to be recognized easily. In the Naruto world, there are many dangerous foes, and wearing a face mask can help him blend in or hide his identity from those who might be targeting him.
Well, it could be about a character in Naruto who has a special mask that somehow gains a malevolent will of its own and starts to 'eat' the face as a metaphor for taking over the character's identity or abilities. Maybe it's a cursed mask that was once used in a forbidden jutsu.
Well, it's hard to say exactly without more context from the fanfic. But it could be that the mask is a sentient object in the story. In the Naruto universe, there are many strange and powerful items. This mask could be trying to take over the character's body by 'eating' their face as a way to gain control. It might also be related to a new enemy or a previously unknown power that the author has introduced.
Sasuke might be the main character. Since he's always on the hunt for power, he might come across this strange mask. And when the mask starts to 'eat' his face, it would be a test of his willpower and his ability to handle the unknown and dangerous forces that come with it.
One creative way to use a Naruto face mask in fanfiction is as a conduit for chakra transfer. Suppose a character is injured and another character uses the mask as a medium to transfer their chakra, kind of like how Naruto sometimes shares his chakra with his friends. The mask could have been specially designed for this purpose by a master ninja. Also, the mask could be a communication device. It has some sort of jutsu - powered technology that allows the wearer to communicate with other characters over long distances, just like how Naruto communicates with his allies during battles.
There might be. Naruto fanfic is a vast genre where writers like to experiment. The Happy Mask Salesman has a rather strange and captivating persona. Some fanfic authors may see the potential in bringing him into the Naruto universe to create new plotlines, perhaps involving strange masks with unique powers in the world of ninjas.
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.
Well, obviously, the addition of the face mask gives him a more mysterious look. His usually open and friendly face is partly hidden, which might make others view him with more caution or curiosity.