Well, there could be a character who was born with a powerful form of aerokinesis but was shunned by society because of it. This character has now turned bitter and blames Naruto for being accepted despite also having aerokinesis. He decides to become Naruto's enemy and uses his power in very destructive ways. Another potential antagonist could be a spirit from an ancient time that has awakened due to Naruto's use of aerokinesis. This spirit is tied to the winds and believes that Naruto is misusing its power. So, it tries to stop Naruto by any means necessary, creating all sorts of challenges for him in the fanfiction.
One potential antagonist could be a rogue ninja who also has aerokinesis but uses it for evil. He might be jealous of Naruto's natural talent and try to undermine him at every turn. Another could be a powerful sorcerer from a far - off land who has come to the Naruto universe specifically to find someone with aerokinesis to either steal their power or use them as a tool. There could also be a group of anti - ninja who see Naruto's new power as a threat to their plans of overthrowing the ninja system and they try to eliminate him.
Perhaps Orochimaru could still be an antagonist. In this fanfiction, he might be jealous of Naruto's new god - like gaming powers and try to steal them for his own experiments.
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.
There could be new antagonists created specifically for this fanfiction. Maybe some other ninja from a far - off land who are jealous of Naruto's power. They could come to the Hidden Leaf Village to challenge Naruto and steal his speed - related secrets.
One potential antagonist could be Orochimaru. He might be interested in Naruto's Mokuton powers for his own evil experiments. He could try to capture Naruto to study how he awakened the Mokuton and use that knowledge for his own gain.
The villagers themselves could be antagonists in a way. Their fear of Naruto's 'demon' side might lead them to try and ostracize or even harm him.
A group of rogue ninjas who have made the island their base could be antagonists. They might see Naruto as a threat to their operations on the island.
One potential antagonist could be Orochimaru. He is always after power and the power of the Nibi within Naruto would be very appealing to him. He might try to capture Naruto to extract the power or use him for his own evil experiments.
In Erza's world, there could be a dark mage who wants to use the power of the unborn child for their own evil purposes. They might see the combination of Naruto's ninja abilities and Erza's magic in the child as a great source of power and will stop at nothing to get their hands on it.
The shinobi clans that uphold the status quo could be antagonists. They fear that Naruto's chaotic power and new ideas will disrupt their way of life. They might try to stop him by any means necessary, including forming alliances against him. They are so entrenched in their old ways that they can't see the potential benefits of Naruto's changes.
There could also be a group that wants to use her child as leverage against her. They might see her love for her child as a weakness and try to manipulate her into doing things that go against her values or the safety of the village.