Obviously, Batman himself is the central character. His complex personality and the situation of being unmasked provide a lot of material for fanfiction writers.
Alfred is another popular character. In the context of Batman unmasked, Alfred has to deal with the fallout. He might be more protective of Bruce Wayne, or have to step in to help Bruce deal with the consequences of his identity being revealed. His loyalty and wisdom play a big role in these fanfiction stories.
Robin is a very popular character. He has a close relationship with Batman, and in fanfiction, their bond can be explored in different ways, like how Robin influences Batman's decisions. Another is The Joker. His chaotic nature makes for interesting interactions with Batman in these stories.
Max is quite popular in 'Batman Beyond Unmasked' fanfiction. She is Terry's friend and often gets involved in his adventures. Her character provides an interesting contrast to Terry's more serious and secretive nature. Another popular character is probably Commissioner Barbara Gordon. She has a connection to the old Batman days and her role in the future Gotham is always an interesting topic in fanfiction.
Iruka Sensei is often included. He might play a big role in taking care of baby Naruto, being like a father figure to him from the start. He could teach baby Naruto basic things like reading and writing in a really cute and heart - warming way.
Amy Rose is often included. She has a long - standing crush on Sonic, so she's a natural fit for the harem concept. Tails might also be included in some more unique takes on the harem, perhaps in a platonic way where he's part of Sonic's support group within the harem. Cream the Rabbit could also be a character in sonic harem fanfiction, adding a cute and innocent element to the harem.
Obviously, Ben Tennyson is the most popular character. He is the main character in the Ben 10 series, and in the gamer fanfiction, he is often the center of the story, using his Omnitrix to fight various enemies. Another popular character is Gwen. Her magical abilities add an interesting dynamic, especially when combined with Ben's alien powers in the context of a gamer - inspired adventure. Also, Grandpa Max is often included as he provides guidance and wisdom to Ben and Gwen during their quests.
Obviously, The Flash himself is a central character. Then there's Iris West, his love interest. Cisco Ramon, with his technological expertise, often plays an important role too. Also, Caitlin Snow, who can transform into Killer Frost, is a popular character in these fanfictions.
Ron Weasley is also popular. He could be a source of comic relief as well as a loyal friend in the new story. If Harry is reborn into a different family or situation, Ron might be one of the first to notice the changes in Harry and help him blend in or deal with any difficulties that come his way.
Catwoman is often paired with Batman in hybrid fanfiction. Their relationship in the original comics is already complex and full of tension. In a hybrid scenario, they could be part of a new species together, like a feline - human hybrid race. This would enhance their connection and the drama between them.
Well, of course, Peter Parker himself is the central character. His aunt May often plays an important role as she has to deal with the new situation of Peter being unmasked and the potential danger it brings to their family.
Ruby Rose herself is, of course, very prominent. Her friends like Weiss, Blake, and Yang are also commonly included. They often play important roles in supporting Ruby or having their own sub - plots that tie into the Rose Arc. Ozpin might also be a popular character as he has a connection to the overarching story and could provide guidance or mystery in the fanfiction.