The Neuralyzer Technician is an underrated but interesting character. Fanfiction could explore his role within the organization. Does he know all the secrets because of his access to the Neuralyzer? There's also the character of Zed. As the head of the Men in Black organization, his leadership and decision - making processes can be delved into. What kind of threats does he see on the horizon that the agents need to be prepared for?
Black Rock Shooter herself is really interesting. Her mysterious past and her incredible power make for great story - telling. Dead Master is also a popular choice. Her dark and somewhat tragic backstory gives a lot of room for creativity. And Strength is another character. Her unique design and her relationship with other characters can be explored in many ways.
Riddick, of course. He's got this mysterious and dangerous aura that makes him really interesting to write about. His past, his abilities, and his moral code all provide a lot of material for fanfiction writers. Another interesting character is Imam. His faith and how it guides him in the face of danger is a great aspect to explore in fanfiction.
Lara Croft from the 'Tomb Raider' series would be a great character to include. She's an expert adventurer and archaeologist. She could help the Men in Black uncover ancient alien artifacts or secrets that are related to current alien threats. Also, Hermione Granger from the 'Harry Potter' series. Her intelligence and knowledge of magic could be applied in unexpected ways in the world of the Men in Black. For example, she could use spells to help in situations where the Men in Black's technology fails.
Agent J and Agent K are usually very popular. Their dynamic relationship has been a staple of the Men in Black series, and in fanfiction, writers often explore different aspects of their friendship and partnership. For example, they might write about their first mission together from a different perspective or how they deal with a personal crisis while on a mission.
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.