It could be a new group of rogue ninjas who have a vendetta against Konoha. They might be led by a powerful and cunning ninja who has a personal grudge against Naruto or the village in general.
Sometimes, in these fanfictions, an old enemy might return in a more powerful form. For example, Orochimaru could come back with enhanced powers and a new plan to destroy Naruto and everything he stands for. He has always been a major threat in the Naruto universe, and in the fanfiction, he could be even more menacing. Another possibility is that a dark and corrupted version of one of Naruto's friends, perhaps Sasuke who has been swayed further to the dark side, becomes an antagonist. Naruto then has to fight back not only against this new threat but also has to deal with the emotional turmoil of facing his once - friend.
There could also be a mysterious and ancient evil force that has been awakened. This force might not be a typical ninja but something more otherworldly. It could be a demon or a dark spirit that Naruto has to fight back against. This would force Naruto to use not only his ninja skills but also his inner strength and willpower to overcome this new and strange adversary.
It could be a group of power - hungry humans who see the Laguz as a resource to be exploited. They might want to use the Laguz's unique abilities for their own gain, like using their strength in labor or their magical abilities for warfare.
It could be a group of rogue ninja who are after the Uzumaki's powerful sealing jutsu. They see it as a way to gain unlimited power and rule the ninja world, so they target the Uzumaki clan, which makes Naruto their main enemy as he stands in their way.
There could be a group of rogue witches and wizards who are against the current system in the wizarding world. They oppose the Ministry of Magic's rules and see Harry Potter as a symbol of the establishment they want to overthrow, so they become the antagonists.
It's hard to say without more details about the fanfiction. But it could be some characters who benefit from Teddy not having rights, like power - hungry individuals or those with prejudiced views.
It could be the village elders. They often have a lot of power and influence in the Naruto universe. If they believe Naruto is a potential threat or they have some ulterior motives, they could be the ones holding him back, thus acting as antagonists.
It could be the same antagonists as in the original Naruto series at first, like the Akatsuki. But if Naruto and Ino change things, new antagonists might emerge. Maybe some ninja who were once allies turn against them because they fear the changes Naruto and Ino are making to the ninja world order.
Since I haven't read it, I can't say for sure. But presumably, Bella is one of the main characters. There could also be other characters like her friends, family, or the antagonists she is fighting against.
Well, the main antagonists could be a group of rogue ninja who are hired by a powerful nation to take down Naruto. Since he is unkillable, they would have to use more underhanded tactics like trying to isolate him from his friends and allies. Or perhaps there is a dark force that is awakened by Naruto's unkillable state, thinking that he is a threat to the balance of the ninja world. This dark force could then become the main antagonist, trying to destroy Naruto at all costs.
Another possibility is that an overzealous member of the Order who has gone too far in their methods of fighting Voldemort. Their extreme actions might make Harry think they have become as bad as the Death Eaters, so he starts to oppose them. For example, if this member starts using unethical spells on innocent people in the name of the greater good.
The main antagonists could be the Sith Lords who are secretly pulling the strings during the Clone Wars. Even though Luke is from a later time, the Sith's influence on the Separatist movement is still a major threat. Darth Sidious, in particular, would be a huge obstacle for Luke. He has his own plans for the galaxy, and Luke's presence could disrupt them. So, Sidious would likely send his minions after Luke and try to eliminate him.