The main characters could really vary. If the 'no life king' concept is about a powerful entity that has been hidden for a long time, it might be that the story focuses on the characters who discover it. So it could be a group of young ninja, perhaps some of Naruto's students or comrades, who stumble upon the mystery of the 'no life king'. And as they try to figure out what it is and how to deal with it, they become the main characters of the fanfiction.
In many Naruto fanfictions, the main characters often include Naruto, Sakura, and Sasuke. So in this 'naruto no life king fanfiction', they could be the main focus as well. However, the 'no life king' element might introduce a new character who becomes central to the story. This new character could be an ancient being or someone who has been affected by this strange 'no life king' power, and their interactions with the original Naruto characters would drive the plot forward.
Sasuke is often a main character in such fanfictions. He could be Naruto's right - hand man, using his skills and intelligence to support Naruto's rule. Their relationship might be more complex, with Sasuke having to come to terms with Naruto's new position of power.
Well, Naruto is likely to be one of the main characters since it's in the title. He would probably be involved in the interactions with the Arrancar King. Sasuke might also be there, as he is a major part of the Naruto story. And of course, the Arrancar King himself would be a central figure, driving the plot forward with his actions and motives.
Naruto is surely a main character. Additionally, there might be some original characters created specifically for this fanfiction. For example, there could be a powerful spirit or a guide in the world of the dead who helps Naruto understand his new powers. And characters like Kakashi could also be involved, perhaps providing advice or assistance to Naruto as he deals with the implications of being the king of the dead.
Since it's a Naruto - related fanfiction, Naruto is bound to be a main character. Regarding the Shadowkhan, there could be a powerful Shadowkhan leader or a group of Shadowkhan who play important roles. Maybe there's a Shadowkhan character who becomes Naruto's ally or rival in his journey to be the king. And of course, Naruto's sensei, Kakashi, might also make an appearance to guide Naruto in this new and strange situation.
Most likely Naruto would be one of the main characters. Since it's in the title, he's probably the central figure in the story.
Obviously, Naruto is one of the main characters as it's about him being the king of foxes. The nine - tailed fox, Kurama, is also likely to be a central figure as it's closely related to Naruto's new title.
Naruto is surely the central character in this fanfiction. Besides, characters like Kakashi could be involved. He might be Naruto's mentor in controlling and understanding his new 'king of fire' powers. And villains from the Naruto universe might also appear. They could be envious of Naruto's power and try to take it away or use it for their own evil purposes. So, a variety of characters from Naruto's world could be main characters in this fanfiction depending on the plot.
It's possible that some new characters are introduced in this fanfiction. They could be powerful underworld figures that Naruto has to deal with. These characters could have their own motives and backstories, and they would interact with Naruto in various ways, either trying to ally with him or overthrow him as the king of the underworld.
The main characters could include a group of thieves, each with their own special skills. For example, one might be an expert in lock - picking, another in distraction techniques. And then there could be the ninja who are after them, such as Kakashi. Kakashi's intelligence and combat skills would make him a formidable opponent in the cat - and - mouse game with the thieves.
Obviously Naruto would be one of the main characters as he is the 'King of Darkness' in this fanfiction. Sasuke could also be a main character as his relationship with Naruto is so central in the original series and would likely be explored in a new way in this dark version. Sakura might also be a main character as she may try to bring Naruto back from the dark side.