In some cases, the antagonist could be the misunderstandings and grudges within the village. These negative elements might have pushed Naruto to become evil. So, in a way, the village's own flaws can be seen as the antagonist. Kushina then has to deal with the consequences of these flaws while trying to save her son from his evil path.
The main antagonist could be the evil Naruto himself. Since he has turned to the dark side, his actions and motives would be against the well - being of the village and those around him, including Kushina. He might be the source of conflict and chaos.
It could also be an outside force that has corrupted Naruto and made him evil. This outside entity could be the real antagonist. Maybe it's a powerful dark wizard or a secret organization that wants to use Naruto's power for their own evil ends. And Kushina has to fight against both this outside force and her own son.
Maybe an ancient evil that has been awakened. This entity is so powerful that it takes the combined godlike powers of Naruto and Kushina to stand against it. The antagonist could have some connection to the origin of chakra or an old, forgotten curse.
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.
The Hidden Leaf Village itself could become the main antagonist. Since Naruto turns evil, the village that once nurtured him would now be against him. The village elders and some of the ninja who oppose Naruto's new evil ways would be in conflict with him. For example, Kakashi might be forced to fight against Naruto to protect the village.
The Hidden Leaf Village itself could be an antagonist. If Naruto goes evil, the village that once was his home would be against him now.
There could also be new characters introduced as antagonists. In this fanfiction, perhaps there are dark entities that are either drawn to Naruto's new evil self or are competing with him for control. They might have powers that rival or complement his Rinnegan - based abilities, leading to some intense battles and power struggles.
The villagers themselves could be the main antagonists. Since Naruto has been neglected, their continued mistrust and hostility towards him could drive his 'evil' turn. They represent the status quo that has failed Naruto, and he might see them as the source of his problems.
Sasuke could also become an antagonist in this scenario. If Naruto turns evil, Sasuke, who has his own sense of justice, would likely oppose Naruto. Their once - strong friendship would be shattered, and they would end up fighting each other, with Sasuke trying to stop Naruto from causing more destruction.
Some members of the ANBU themselves could be antagonists. They might think that Naruto belongs with them and that Kushina is interfering in their affairs. They could try to keep Naruto in the ANBU by any means necessary, including using force or setting up traps for Kushina when she tries to approach Naruto.
The Akatsuki as a whole could be antagonists. In fanfictions, the Akatsuki might be interested in the power of Naruto's Evil Rinnegan. They could try to capture him to extract the power or use him in some way for their own goals. Pain, being a powerful member of the Akatsuki, could also be a specific antagonist. His own ideology about pain and peace might clash with Naruto's new, potentially more chaotic state with the Evil Rinnegan. Additionally, new original antagonists created specifically for the fanfiction could be common. These could be dark, powerful figures who are drawn to the power of the Evil Rinnegan and want to either possess it or destroy Naruto to prevent its misuse.
Often, it portrays a very strained relationship. Naruto is likely to be confused and hurt by his mother's evil actions. He may try to reason with her at first, believing that there is still good in her.