The Orochimaru could be a great main antagonist. He's always been interested in power and new forms of combat. In a fanfiction, he could get his hands on some Command and Conquer technology and use it to create his own army of powerful, mutated creatures. He might even try to take over the ninja world using these new forces, and Naruto would have to stop him.
It could be an original character. Maybe a rogue ninja who has been secretly studying the secrets of Command and Conquer in a different dimension. He comes back to the ninja world with advanced knowledge and technology. He starts to build his own empire, enslaving smaller villages and forcing them to work for his military machine. Naruto would then have to rise up against this new threat and free the ninja world from his tyranny.
The main characters likely include representatives from the GDI and the Brotherhood of Nod.
Well, Kane is a central figure in the Command and Conquer Tiberium Wars story. He's the leader of the Brotherhood of Nod and has a mysterious and somewhat fanatical following. For the GDI, apart from General Jack Granger, there are also other important characters like Colonel James Solomon. He is involved in many key battles and strategic decision - making processes. These characters drive the story forward through their actions, beliefs, and the conflicts between them.
Well, in these fanfictions, you often see a blend of the two worlds. The technology or strategic concepts from Command and Conquer are incorporated into the Harry Potter setting. So, you might have things like Hogwarts being fortified like a Command and Conquer base. Also, the relationships between characters might change as they adapt to this new, more strategic environment. The magic system could also be tweaked to fit the more strategic narrative, with spells being used for more than just everyday magic but for large - scale battles and defenses.
A possible plot is that Naruto discovers a strange portal that leads to the world of Command and Conquer. He teams up with some of the game's factions to learn their combat strategies and bring them back to the ninja world. He could then teach his friends how to use these new tactics, like building fortifications and using combined arms warfare. Or perhaps there is a villain in the Command and Conquer world who wants to invade the ninja world, and Naruto has to lead the defense using a mix of his ninja skills and the new technology he has learned.
It could be someone from the Naruto universe who doesn't like Naruto's newfound fascination with Aku. For example, Danzo might see Naruto's interest in Aku as a threat to the stability of the village and try to stop Naruto from further exploring Aku - related things. So, Danzo could be the main antagonist in this case.
Maybe a new character could be introduced as the main antagonist. This character could be from a hidden village that has been secretly observing Naruto's growth. They realize his potential as a weapon and plan to steal his power or use him to start a war against other villages.
Krampus himself could be the main antagonist. Since he is a figure known for punishing the naughty, his actions in the Naruto world might be seen as unjust. He could be going after ninjas without really understanding their motives, causing a lot of trouble for the main characters.
It could be a rogue ninja who also has somehow acquired bankai - like powers. This antagonist might be jealous of Naruto's newfound abilities and wants to prove that he is the stronger one. So he starts causing chaos in the ninja world, challenging Naruto at every turn.
It could be a rogue ninja who wants to disrupt Naruto's business to gain power. Maybe he's jealous of Naruto's success and popularity in the business world. He could try to steal Naruto's business secrets or sabotage his operations.
It could be a rogue Kumo ninja who is jealous of Naruto's power and wants to prove himself by defeating Naruto. This ninja might have some dark secrets and a grudge against Kumo as well.