Who could be the main antagonist in 'anime war infinite fanfiction'?

It could be a jealous ninja from another village who sees Naruto's infinite chakra as a threat to their own village's power. This ninja might try to steal Naruto's chakra source or find a way to nullify it.

Dr. Eggman could be a great main antagonist. He could be using the chaos of war to further his own plans for world domination. He might be creating powerful war machines and using them to take over different regions, forcing Sonic and his friends to fight back to protect the peace.

It could be a power - hungry general from one of the warring factions. Someone who is willing to sacrifice anything and anyone to achieve victory.

It could be an alternate version of herself from a dark dimension. This Gwen has turned evil due to some tragic events in her world and wants to conquer the entire Omniverse, seeing the normal Gwen 10 as a threat to her plans.

A rogue ninja from a formerly warring village could be the main antagonist. This ninja might hold a grudge against the new peace and wants to disrupt it. He could be powerful and have his own group of followers who are also discontent with the current situation.

A powerful and corrupted duelist from a forgotten dimension could be the main antagonist. This duelist might have discovered a way to harness the power of the dimensional rifts for his own evil purposes. He could be using this power to create chaos and destruction across all the dimensions, and only the combined efforts of the heroes from different dimensions can stop him.

Madara Uchiha could be a great antagonist in this kind of fanfiction. He has the power and the ambition. He could manipulate the war game from behind the scenes, perhaps using his Sharingan to control the minds of some of the participants. He wants to reshape the ninja world according to his own vision, and the war game provides him with an opportunity to do so without directly confronting all the ninja forces at once.

It could be a powerful vampire from a different coven. Maybe one who sees the daughter of war as a threat to their power or territory in the Twilight world.

A new supervillain could emerge. Maybe a scientist who got access to some of the leftover technology from the Civil War battles and uses it to create a powerful weapon. He then targets Spiderman because he represents the superhero community.

It could be a Miraculous holder who has been corrupted by the power. They might start to think that they should be the sole leader and use the civil war as a means to take over. For example, if a holder of a powerful Miraculous like the Bee Miraculous turns bad, they could be a formidable antagonist.