Obviously, Draco Malfoy is a main character. He is central to any story about his collar as it is something directly related to him. Hermione Granger could also be involved. She might be curious about the collar's magic or purpose and try to study it, which could lead to some interesting interactions between her and Draco.
Hermione Granger could also be a main character. She might be the one who discovers Draco in shackles and uses her intelligence to figure out how to free him or to use his situation to gain some knowledge about the Death Eaters. Her presence can bring a different perspective to the story.
Some fanfictions might also involve the villains. Voldemort or his Death Eaters could be interested in the bound collar for their own evil purposes. They might try to steal it or use it against Harry and his friends, which would create a lot of conflict and action in the story.
Draco Malfoy and Argus Filch are the main characters. In these fanfictions, Draco might be exploring the secrets of the collar out of curiosity or for some devious plan. Filch, on the other hand, is protective of his collar as it might hold sentimental value or some power that he doesn't want to be misused. There could also be minor characters like the Weasley twins. They could be causing additional chaos while Draco is dealing with the collar situation, perhaps using it as an opportunity to play more pranks in Hogwarts.
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.
Draco Malfoy is, of course, the main focus. However, his family members like Lucius and Narcissa Malfoy are often included. They can either contribute to his collapse, for example, through their high - handed family ways, or be part of his support system (although in many cases it's the former). And sometimes, characters like Snape might be involved too, as he has his own complex relationship with Draco and the whole Slytherin house.
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.
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.
Bella and Edward are often main characters in such fanfiction. Since their relationship is central in the original Twilight series, in fanfiction about sacrifices, they could be the ones making sacrifices for each other. For example, Edward might sacrifice his vampiric nature to give Bella a more 'normal' life if she so desires.
Naruto himself is obviously a main character in such fanfictions. His growth in intelligence is usually the central focus. Sasuke can also be involved as Naruto's rival or ally in situations where intelligence plays a crucial role. Sakura, with her own intellectual capabilities in medical ninjutsu and general knowledge, often appears as well.
Sasuke is also commonly involved. His own journey of self - discovery and redemption is a rich area for fanfiction writers. His complex past and his actions that have caused harm in the Naruto world make his redemption arc an interesting topic to explore, especially in relation to how he reconciles with Naruto and the rest of the village.