Well, obviously the archangels like Michael, Lucifer, and Gabriel are often main characters. Michael is usually portrayed as a very powerful and somewhat rigid character, so seeing him without his grace can be a really interesting transformation. Lucifer, on the other hand, is always a complex character, and his actions when he loses his grace can be very unpredictable.
Sometimes, other angels like Castiel could also play a role. He might be in a position to either help or hinder the graceless archangels. Maybe he has some knowledge about how to restore grace, or he could be trying to keep the balance in the angelic hierarchy in the face of the archangels' new situations.
One possible plotline could be an archangel struggling to survive in the human world without their grace. They might have to learn how to do things the human way, like getting a job or finding shelter. For example, Michael could be stripped of his grace and end up working at a diner, trying to figure out how to blend in.
Castiel can also be a major character in these fanfictions. His relationship with Gabriel as an angel could bring in some interesting dynamics. They might work together or have some sort of conflict based on their different views and experiences. Also, Crowley could potentially be involved, as he often had his fingers in various supernatural pies in the series. His devious nature could either help or hinder Gabriel's plans upon his return.
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.
Another possible main character could be Crowley. He might be interested in Gabriel's wings for his own devious reasons. Maybe he wants to use the power of the wings for his own gain or to gain an advantage over other demons. His interactions with Gabriel in relation to his wings could create some interesting plot twists and turns in the fanfiction.
Naruto himself is often a central character in 'naruto destruction fanfiction'. Since he is the main protagonist of the original series, fanfiction writers like to put him in situations where he has to deal with destruction. Sasuke is also frequently involved as his rival, and their relationship can be explored in the context of destruction, like if they have to work together to stop a greater threat of destruction.
Obi - Wan Kenobi is frequently in Anakin Snaps fanfiction. As Anakin's master, he has a big role to play. Their relationship is often explored, and Obi - Wan's reactions to Anakin's snapping are crucial. Sometimes he tries to bring Anakin back from the brink, while other times he might be the cause, albeit unintentionally, of Anakin's breakdown.
Well, Naruto is obviously a main character in most of these. But there could also be Sasuke. He might be either an ally or an adversary in relation to the dagger. For example, if the dagger has a power that can either be used for good or evil, Sasuke could be tempted by its darker potential.
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.
Obviously, the Reaper is a main character. Ruby Rose is also often involved as she is one of the central characters in RWBY and her connection to the concept of death (which the Reaper represents in a way) makes for interesting interactions. Weiss Schnee can also be seen in some fanfictions, as her family's past and her own story can cross paths with the Reaper's storyline in creative ways.
Some fanfictions might also include characters like Kakashi in important roles. As Naruto's former teacher, he could be a guiding figure or someone who has to adapt to Naruto's new level of power. He might also be involved in trying to keep Naruto's power in check if it starts to have negative effects on the ninja world.