In this type of fanfiction, it's possible that some of the main antagonists are actually old enemies who have now also developed or mastered killing intent. For instance, Orochimaru might have further enhanced his abilities and now poses a greater threat to Naruto with his own version of killing intent. Or it could be some of the Akatsuki members who, after seeing Naruto's new power, become more determined to defeat him and claim his power for themselves.
It could be characters who are also masters of killing intent and oppose Naruto for various reasons, perhaps power struggles or ideological differences.
Well, Naruto is surely one of the main characters as the title implies his mastery of killing intent. There might also be Sasuke, as he is Naruto's long - time rival and friend. Sakura could be there too, as she is part of Naruto's main group. And perhaps some of the older characters like Kakashi or Jiraiya might make an appearance to guide Naruto in his journey related to the killing intent.
One interesting aspect could be how Naruto's character is developed in relation to the 'master of killing intent' concept. Maybe he uses it in unique battles or it changes his relationships with other characters.
Well, it could be about Naruto developing an extreme level of killing intent. Maybe it shows how he uses this powerful intent in battles, perhaps against new and dangerous foes. It might also explore how this aspect of his character affects his relationships with his friends and allies in the Naruto universe.
There could be a jealous fellow ninja from within the village who feels that Naruto is getting too much attention for his blade - mastery. This ninja could turn against Naruto and become an antagonist, perhaps even teaming up with external forces. Also, an ancient evil entity that was sealed away long ago might be awakened by the power of Naruto's blade and seek to destroy him and the village to regain its freedom.
It could be a group of rogue ninja who are jealous of Naruto's new powers. They might band together to try and steal his knowledge of all ninja arts or defeat him to prove their own superiority.
Well, Naruto is surely one of the main characters since it's in the title. He's the one who's supposed to be the master of silent killing in this fanfiction.
Well, the main antagonists could be a group of rogue ninja who are hired by a powerful nation to take down Naruto. Since he is unkillable, they would have to use more underhanded tactics like trying to isolate him from his friends and allies. Or perhaps there is a dark force that is awakened by Naruto's unkillable state, thinking that he is a threat to the balance of the ninja world. This dark force could then become the main antagonist, trying to destroy Naruto at all costs.
Maybe there are powerful dark sorcerers. These sorcerers could be trying to capture Naruto for their own evil purposes, like using his power to open a portal to a dark dimension or something, and Kurama has to protect him from them.
Another type of antagonist could be a strict professor who doesn't like Naruto's carefree attitude and Hinata's association with him. The professor might try to give them a hard time, like assigning them extra difficult projects or being overly critical in class, which becomes an obstacle in their college life and relationship.
Anko might not be a traditional antagonist, but if she is siding with Evil Naruto for some reason, she could be seen as an antagonist from the perspective of the other villagers. However, it's also possible that she is being manipulated herself, in which case the true antagonists would be those doing the manipulating.