There could be a mysterious figure from Naruino's past during the war. This person has a grudge against Naruino and resurfaces in the post - war period to seek revenge, creating all sorts of problems for Naruino.
Another option for antagonists could be a new organization that rises in the power vacuum left after the war. They might have different ideologies from Naruino and his village. For example, they could believe in total domination rather than the peace and co - existence that Naruino stands for. They would see Naruino as a threat to their plans and try to eliminate him.
It could be about Naruino rebuilding his life. Maybe he starts a new business in the post - war era, using his skills to contribute to the reconstruction of the village.
One possible plot could be that Naruino, having survived the war, now focuses on rebuilding his village. He uses his unique skills and experiences from the war to improve the village's defenses and also to teach the younger generation how to protect themselves. For example, he could set up a training academy where he imparts his combat knowledge and ninja techniques.
It could be a rogue ninja who was once part of a minor group during the war but has now risen to power. Maybe they felt overlooked or mistreated during the war and now seek revenge on the major villages.
It could be a rogue vampire who didn't like the way the war ended and blames Alucard and Seras. This vampire might have his own ideas about how the vampire world should be ruled and sees them as obstacles.
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.
Mr. Sinister could be a great antagonist. He's always interested in mutant genetics and power. He could be the one secretly pulling the strings, making Cable and Deadpool believe they need to fight over the future of mutantkind. He could plant false evidence or use his mind - control abilities on some of the supporting characters to fuel the conflict.
A group of former war criminals who were pardoned but now want to take over the ninja world. They might have formed a secret organization during their time in prison or exile. They could be using new, dark jutsus that they developed in secret to try and overthrow the current leadership in the villages and establish their own rule.
It could be a power - hungry politician who wants to use the Hulk as a weapon to gain more control during the Civil War. This person might not care about the destruction the Hulk could cause, just as long as they achieve their own goals.
It could be Mysterio. He's known for his illusions and deception. In the context of a civil war, he could use his powers to create false scenarios that make the heroes fight each other even more. He might pretend to be a hero on one side, but secretly be working to make the conflict worse for his own gain.