Well, in a lot of Oblivion Dark Seducer fanfiction, the main characters would include the Dark Seducer, of course. Then there could be other Daedric creatures like the Xivilai who might interact with the Dark Seducer. And sometimes, mortal characters who get caught up in the Dark Seducer's schemes, like a brave knight or a cunning thief, could be main characters as well. The relationships between these different characters can create really interesting storylines.
The Dark Seducer is the central figure. However, other characters such as the Daedric Prince Sheogorath could be involved. In some fanfiction, Sheogorath might play a role in the Dark Seducer's story, perhaps using the Dark Seducer for his own mad purposes. Also, there could be a mysterious wizard character who tries to control or understand the Dark Seducer, adding more depth and conflict to the fanfiction.
The Dark Seducer themselves are obviously a main character. Often, the player character from Oblivion might be involved as they interact with the Dark Seducer. Another could be Mehrunes Dagon, as the Dark Seducer has ties to the Daedric Princes.
One interesting concept could be the exploration of the Dark Seducer's origin. Maybe in the fanfiction, it delves into how they came to be in the world of Oblivion. Another concept might be their relationships with other characters in the game's lore, like how they interact with the Daedric Princes or mortal characters.
There can be original characters created specifically for the fanfiction. For instance, a detective who is obsessed with bringing down the Joker but slowly starts to lose his own sanity in the process. This character can provide a new perspective on the Joker's reign of terror.
Varian is, of course, the main focus. However, characters like Eugene could also be involved. He might be in a more antagonistic role towards Varian in this type of fanfiction, trying to protect Rapunzel from what he perceives as Varian's dangerous actions.
The Nine - Tails also plays a major role. In a dark Naruto story, the Nine - Tails could be more of a corrupting influence, whispering dark thoughts into Naruto's mind and fueling his descent into a more menacing figure in the ninja world.
Naruto himself could be a main character. He might be tempted to use dark summons to gain power to protect his village or friends. For instance, in some fanfictions, he discovers a dark summon that could potentially defeat a powerful enemy threatening Konoha, but at a great cost.
In Naruto dark chakra fanfiction, Sasuke is frequently a central figure. Given his complex character arc and his inclination towards power - seeking, it's easy to envision him being affected by or exploring dark chakra. Naruto too can be a main character. His strong will and connection to positive chakra could be put to the test when faced with the allure of dark chakra. Another character often involved is Kabuto. He has a history of being involved in dark and underhanded schemes, so it's not a stretch to see him in stories centered around dark chakra. There are also some original characters created by fanfiction authors that are specifically designed to interact with the concept of dark chakra in unique ways.
Naruto himself is often a main character. He's usually the one who stands up against the dark guild's evil plans. Sasuke might also be involved, as his power and sometimes ambiguous moral standing can add interesting dynamics when dealing with the dark guild.
Obviously Naruto himself is a main character as he is the one under the dark control. Then there would be his friends like Sasuke and Sakura. Sasuke might be crucial in trying to understand and counter the dark power since he has his own powerful abilities.
Well, obviously Dark Silver himself is a main character. Often Sonic might also be involved as he is a central figure in the Sonic universe. Their interactions can create interesting storylines, like a rivalry or an uneasy alliance.
Naruto himself is often involved. He might be either tempted by Dark Hadou or have to fight against those who use it. Sasuke could also be a main character in such fanfictions. His quest for power could lead him to explore the Dark Hadou. And then there's Kakashi, who with his experience and knowledge, might be involved in trying to stop the spread of Dark Hadou.