Definitely Kara Zor - El herself. Writers can explore different facets of her personality, from her vulnerability as an alien trying to fit in on Earth to her great strength as a superhero. They can also play with her relationships, like with her sister Alex, which can add a lot of depth to the story.
One of the most interesting characters is often Nurgle himself. His grotesque and complex nature makes him a fascinating subject. He is both a bringer of disease and decay, yet also represents a sort of twisted form of life. Another interesting character can be the Plaguebearers. These are his minions, and in fan fiction, they can be depicted in different ways, sometimes with a bit of individuality among them. Then there are the Champions of Nurgle, humans who have given in to his power. Their internal struggle between their former selves and their new, corrupted selves can make for very engaging stories.
Shadow is often really interesting in fan fiction. His complex past and his brooding personality make for great storylines. Silver is also cool, especially when his time - traveling abilities are explored in different ways.
Chunk is always a great character to include. His funny and sometimes clumsy nature can add a lot of humor to the story. For example, he could accidentally trigger a booby - trap while the Goonies are exploring a new cave, but then also be the one to find a way out of it in a really unexpected way.
Definitely Xena and Gabrielle are among the most interesting. But in alt fan fictions, some writers introduce a mysterious figure from Xena's past, perhaps an old enemy or a long - lost friend. This character can add a whole new layer of mystery and drama. Also, there are often characters that are hybrids of different species in the Xena universe. These unique creations bring in elements of the supernatural and the unknown, making them very engaging in the fan - written stories.
In swtor companion fan fiction, Doc is quite an interesting character. His medical skills and his often - comical remarks can add a lot of flavor to a story. Kira Carsen is also great. Her journey from being a Jedi padawan to a more experienced warrior can be delved into deeply. And don't forget about Vector Hyllus. His hive - mind connection and his gentle nature make him stand out among the companions in fan fictions.
Obviously, Supergirl herself should be included. Her presence can add more drama and conflict, especially if she has mixed feelings about Lena and Mon - El's relationship. J'onn J'onzz could also be a great addition as he can offer his wisdom and alien perspective.
I think the newly - turned Black Spiral Dancers can be really interesting. They still have some memories and emotions from their previous lives, which creates a lot of tension. They are caught between their old selves and the new, dark path they are on. For example, they might struggle with the new urges to hunt and kill that go against their former moral compasses. This makes for some great character - driven stories in the fan fiction.
I think the antagonists in 'the gifted fan fiction' can be really interesting to write about. They often have complex motives for their actions. Maybe they are using their powers for a cause they believe in, but that goes against the heroes' values. Their backstories and how they came to be the way they are can add depth to the fan fiction. Also, the side characters with more subtle powers can be great to write about as they can surprise readers with their abilities in unexpected situations.
Mal is definitely one of the most interesting. She has such a complex personality, being the daughter of Maleficent. There's a lot to explore in terms of her struggle between her mother's dark legacy and her own desire to be good. Evie is also great. Her journey from being a'spoiled' princess - type to someone more independent and kind - hearted can be really fun to write about. And then there's Jay, with his thieving ways but also his potential for growth and loyalty.
Rey is an obvious choice. Her journey from a scavenger to a powerful Jedi is full of potential for further exploration. You could write about her internal struggles with her newfound power and her place in the galaxy. Finn is also interesting. His growth from a stormtrooper to a Resistance hero can be delved into deeper. For example, his experiences in the First Order and how they still affect him during the fight against Palpatine.