Definitely Reese. He has such a complex personality. He's often the troublemaker, but there could be so much more to him. Fanfiction writers can explore his insecurities behind his tough - guy act. Lois is also a great character to write about. Her strong - willed and no - nonsense attitude can be the center of many stories. You could write about how she manages the family's finances even tighter or how she disciplines the boys in new and different ways.
Hal is also a great character to focus on. His zany antics and his relationship with his wife and sons can be a source of many interesting stories. For example, a fanfic could be about Hal trying to plan a surprise for Lois and all the chaos that ensues.
A crossover with 'Stranger Things' would be cool too. Picture Malcolm and his brothers getting caught up in the Upside Down mystery. They could use their own brand of mischief - making skills to survive and figure out what's going on in that strange parallel dimension.
Circe is a very interesting character for greek fanfiction. She has the power of magic and transformation. Writers can explore how she uses her powers to manipulate those who come to her island. Also, Odysseus is a classic character that is always interesting to write about in new ways. His long journey home can be reimagined, or his interactions with other mythological beings can be expanded upon.
Gerry is definitely one of the most interesting. His unique love for animals and his innocent yet inquisitive nature offer a lot of room for creativity. Writers can create all kinds of scenarios where Gerry discovers new species or has heart - warming interactions with the local wildlife.
Alice is a very interesting character to write about. Her ability to see the future gives so many possibilities for plot twists. Writers can explore how she might use or be haunted by her visions in different situations. Another is Jasper. His past as a Confederate soldier and his struggle with his bloodlust can be delved into deeply.
For me, Sol Star is an interesting character to write about in deadwood fanfiction. He's often in the background but has his own dreams and desires that can be further developed. Then there's E.B. Farnum. His conniving and somewhat pathetic nature can be a source of great comedic or tragic stories. And of course, Wild Bill Hickok. His legend and his short time in Deadwood provide a lot of inspiration for different storylines.
Link is a very interesting character. His complex backstory with the Triforce and his many adventures in Hyrule give a lot of material for fanfiction. You can write about his internal struggles, like when he has to make tough decisions to save his kingdom. Another interesting one is Kirby. His cute appearance but powerful abilities create a contrast. You can write about Kirby exploring new planets and befriending other SSB characters.
In my opinion, the Death Knight can be a very interesting character for quake fanfiction. It has this dark and menacing presence. You could write about its past, like how it became this powerful and feared entity. Another interesting character is the Fiend. You can explore its relationship with other creatures in the Quake world, or how it hunts its prey. And the Vore is also an interesting one. It has this unique and grotesque appearance, and you could write about how it came to be in the Quake universe.
Yato is definitely one of the most interesting. His complex personality, with his past as a war god and his current quest for recognition, gives a lot of material for fanfiction. Hiyori is also great. Her ability to cross between the worlds and her kind - hearted nature make her a fascinating character to explore in different scenarios. And Yukine, with his growth as a shinki and his relationship with Yato, offers a lot of potential for interesting stories.
Elise is a really interesting character to write about. Her grace and skill on the slopes make for great descriptions. Mac is also cool. His laid - back attitude combined with his amazing stunts gives a lot of material for fanfiction. And then there's Zoe. Her bubbly personality and determination can add a lot of charm to a story.