Often, the Straw Hat crew members are also main characters. They are closely associated with Luffy. For instance, Zoro might be there to protect Luffy when the mask causes some unexpected trouble. Nami could be involved in trying to figure out the value or origin of the mask, as she is interested in treasures.
Well, of course, Luffy is always one of the main characters. And then there's usually an admiral, like Akainu or Kizaru. They often start as antagonists to Luffy but then the story might develop their relationship in different ways.
Often, Harry, Hermione, and Ron are still main characters in 'Harry Potter Mask Fanfic'. They might be the ones to discover the mask and its powers. Neville could also be a main character, perhaps using the mask to gain confidence and show his true potential. And sometimes, even Draco Malfoy could be involved if the mask has something to do with the Slytherin side of the wizarding world.
I don't know for sure as it depends on the specific fanfiction. But it could be Stanley Ipkiss, the main character from 'The Mask' movie. He's the one who typically dons the mask and goes on wild adventures.
Well, there could be a luffy mask fanfiction where the mask is a magical heirloom. In this story, Luffy discovers that the mask has a connection to an ancient civilization. As he wears it, he starts to have visions of the past and gains knowledge that helps him find a hidden treasure. This treasure not only enriches the Straw Hat crew but also helps them make new allies in the strange new islands they visit.
Obviously Naruto is one of the main characters. And the owner or creator of the mask could also be a main character, whether it's a new character introduced in the fanfiction or an existing character with a new role related to the mask.
In luffy x mihawk fanfiction, the central characters are Luffy and Mihawk. Luffy, with his signature straw hat and his devil - fruit - given powers. He has a heart of gold and is always looking for adventure. Mihawk, with his black sword Yoru. He is a figure of great mystery and power in the One Piece world. Their different personalities and goals are what make their relationship in fanfiction so interesting to explore.
In 'Shanks Saves Luffy' fanfiction, Shanks and Luffy are the central figures. However, characters from Shanks' crew could also be involved. They might be there to assist Shanks in the rescue mission or have some sort of back - story related to why Shanks is so determined to save Luffy. Additionally, any new characters created specifically for the fanfiction, perhaps a powerful being who is the root cause of Luffy's danger, could also be main characters in the story.
It's Luffy and Zoro. Luffy is known for his carefree and fearless attitude. He can be quite silly at times but is also extremely brave. Zoro is the more serious one among them, though he also has his humorous side. In the 'Luffy naps with Zoro fanfiction', their interactions during the nap would be interesting to explore.
Well, there could also be some side characters from both Amazon Lily and the places the Straw Hat Pirates have visited. For example, the Kuja warriors from Amazon Lily could be there to celebrate the marriage. And from Luffy's side, maybe some of the friends they made in different islands like the people from Dressrosa or Alabasta could also make an appearance in the fanfiction to add more flavor to the story.
Robin is also an important member of the Straw Hat Pirates. She is an archaeologist with the ability to sprout body parts from any surface. She is very intelligent and her knowledge of history and ancient things often comes in handy during their adventures. In the fanfiction, she and Luffy are likely to have some special interactions and storylines.