Definitely Dean and Sam are among the most popular. Their brotherly bond is a central part of Supernatural, and when one or both are genderswapped, it allows for a whole new exploration of that bond. But characters like Bobby Singer can also be interesting when genderswapped. A female Bobby could have a different nurturing side while still being the tough mentor figure. And then there's Rowena. A male Rowena would be an interesting take, as her powerful witch character could be reimagined with a male perspective, changing her relationships and the way she wields her magic in the fanfiction.
Dean Winchester is quite popular to be genderswapped. His strong personality and complex backstory make for an interesting female version. People like to explore how a female Dean would interact with the other characters, especially Sam. Sam Winchester is also a common choice. A genderswapped Sam can bring new perspectives to the story.
Castiel is another character that is often genderswapped in this type of fanfiction. His angelic nature combined with a gender change can lead to some really unique storylines. Fans enjoy imagining how a female Castiel would fit into the Supernatural universe, how her relationships with Dean and Sam would evolve, and how her angelic powers might be perceived differently. And of course, Crowley has also been genderswapped in some fanfictions. A female Crowley could have a different approach to ruling Hell and interacting with the Winchesters.
Castiel is also a favorite. His angelic nature and his complex relationship with the Winchesters can take on new dimensions in inflation fanfiction. For instance, if there's an inflation of angelic powers, how he navigates that while still being involved with Sam and Dean makes for great story material.
The witches are often popular. They have a lot of powers and can be both good and bad, which gives a lot of room for character development. For example, a witch might start off using her powers for selfish reasons but then learn to use them for the good of the community.
Abaddon is often a popular 'Knight of Hell' character in fanfiction. Her strong and devious nature makes for great storytelling. Writers can explore her backstory more deeply, like her rise to become a Knight of Hell and her motives for causing chaos in the Supernatural world.
Sam and Dean Winchester remain popular as well. Their relationship with Chuck, whether it's one of loyalty, betrayal, or a complex mix, is often explored. They are the main protagonists of the original series, and in these fanfictions, their reactions to Chuck's true identity are key elements.
One common theme is relationship exploration. With genders swapped, the relationships between characters like Sam and Dean, for example, take on new dimensions. Another is power dynamics. Female - swapped versions of male characters might face different challenges in a male - dominated world within the Supernatural universe.
Batman is definitely a popular choice. His detective skills would be very useful in dealing with supernatural mysteries. He could use his knowledge of Gotham's history and its hidden secrets to figure out what's going on when faced with supernatural threats.
One interesting concept is how the characters' relationships change. For example, if Dean was gender - swapped, his dynamic with Sam might have new emotional undertones. Another concept could be how the genderswapped character approaches hunting. A female Dean might use different tactics or have different insecurities in a male - dominated hunting world.
Sam and Dean Winchester are always popular in Supernatural fanfiction, including those based on 13x17. Their brotherly bond and their roles as hunters are often central to many stories. Castiel is also a favorite. His angelic nature and his relationship with the Winchesters make him a great character to write about in relation to the events of 13x17.
Issei Hyoudou is often a popular choice. He's the main character in the original series, so there's a lot of material to draw from and expand on. Writers can explore his growth as a character, his relationships with other characters, and his development of new powers.
In some of these fanfictions, Ruby can be a popular character. She has her own history with the Winchesters and with the underworld. When a daughter of hell is introduced, Ruby's knowledge and her own motives can make for some interesting plot developments. And then there's also Rowena, a powerful witch. Her magic and her devious nature can create all sorts of trouble and alliances when combined with the presence of a daughter of hell.