Alina is also frequently involved. Her connection to the Darkling in the original work makes her a natural addition in many fanfictions. Their complex relationship can be further explored or even rewritten in different ways in fanfiction.
Then there are other Grisha characters. They might play different roles depending on the plot of the fanfiction. For example, some might be loyal allies of the Darkling, while others might oppose him. Their powers and personalities add depth and variety to the stories.
Obviously Naruto himself is a main character. He is the one with the pacemaker so he is central to the story. Sasuke might also be involved. He could be initially skeptical of Naruto's new situation with the pacemaker but then come around to help. Sakura too, as a medical ninja, she could play a crucial role in understanding and perhaps even trying to modify the pacemaker.
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.
Well, obviously Gaster is the central character as it's about his pregnancy. But often, other characters from the same fictional world might be involved. For instance, characters who are friends or colleagues of Gaster could be there to support or oppose the situation. It might also include characters who have some sort of special connection to Gaster's unborn child, like a potential mentor or an enemy who wants to harm the baby.
The dragonborn himself is, of course, a main character in these fanfictions. Depending on the story, other DxD characters like Akeno Himejima could also be involved. She has her own powers and personality, and her interactions with the dragonborn can add a lot of depth to the story. Her seductive nature might play off against the dragonborn's more straightforward and perhaps stoic personality.
Naruto is almost always a main character in 'naruto dice fanfiction' as the story is based on the Naruto universe. His friends like Sasuke and Sakura also often appear. Sasuke's cool and brooding nature can add an interesting dynamic when combined with Naruto's more upbeat and impulsive personality in stories related to the dice.
Klaus Mikaelson is usually a central figure. His complex character and his role as a father in the fanfiction can lead to many interesting story developments. His relationship with the baby can range from over - protective to conflicted, depending on the plot.
Obviously, Goku is the main character. But sometimes, characters like Vegeta might also be involved. Vegeta could be either an ally trying to help Goku deal with his vampire side or a rival who sees Goku's new form as a threat.
Kakashi could be a central figure in such fanfiction. His Sharingan and combat expertise would make him an interesting character to be associated with a special knife. He could use his knowledge to teach others about the knife's proper use. Another character could be Sakura. If she gets hold of a knife with unique healing properties, she could use it to both heal and fight, adding a new dimension to her character in the fanfiction.
Well, Mikasa herself is obviously a main character in these fanfictions. Since it's about her snapping, she is at the center of the story most of the time. Eren is also often involved. Given their complex relationship in the original series, his actions or words could be the trigger for Mikasa to snap. Another character that might be involved is Armin. He could be the one who tries to calm Mikasa down or understand what made her snap.
Well, the Necrofriggian Babies themselves are obviously main characters. They are the focus of the story, and their actions and experiences drive the plot.