Perhaps it's a member of a secret organization that has ties to Naruto's family. They see Naruto as a threat because of his potential connection to his family's heritage. They try to manipulate the situation and the villagers to keep Naruto down and isolated so that he can't uncover their plans.
In this fanfiction, the main antagonist might be a powerful ninja who has a vendetta against Naruto's family. Since Naruto is part of that family, this ninja targets him. He uses Naruto's abandonment as a way to further isolate and weaken him, all while trying to achieve his own goals which might involve taking over the village or obtaining some powerful jutsu that is related to Naruto's family.
It could be a relative from his family who was behind the abandonment. Maybe they want to keep Naruto away from some family secret or power, and they will do anything to stop him from finding out the truth.
The main antagonist might be a dark wizard or sorcerer who has a long - standing feud with the dragon. When Naruto is abandoned and finds the dragon, this antagonist sees Naruto as an easy target to get to the dragon. They might try to manipulate Naruto or directly attack him to get the dragon under their control. Also, it could be a group of rogue ninjas who want to use the dragon's power to take over the ninja world and view Naruto as a hindrance since he has a bond with the dragon.
Maybe it's an evil organization that wants to isolate Naruto. By making his family forget him, they hope to break Naruto's spirit and prevent him from becoming a powerful force in the ninja world. So they target his family's memories as a way to get to him.
It could be the elders of his clan. They are often the ones who make decisions in the clan, and if they see Naruto as a threat for whatever reason, they could be the main antagonists. They might be afraid of Naruto's growing power or his different way of thinking that could disrupt the traditional ways of the clan.
It could be Danzo. He's always been a bit of a shadowy figure in the Naruto series. Maybe he sees Naruto as a threat to his power and influence in the village and manipulates the situation so that Team 7 has to abandon him. He would be a great main antagonist as he has the resources and the motives to cause such a rift in Team 7.
Maybe the main antagonist is the entire Iwa council. They might be the ones who order Naruto's abandonment because they fear his potential influence on Iwa. They would do everything in their power to keep him from uncovering their plans or causing unrest among the villagers.
The Akatsuki could be the main antagonist. They might see Hanzo as an easy target after Naruto abandons him and try to capture him for their own purposes, like using his knowledge of the ninja world or his unique abilities.
It could be someone from the village who doesn't want Naruto to discover the truth about his parents. Maybe they fear that if Naruto finds out certain secrets, it will disrupt the power balance in the village.
It could be a powerful and jealous trainer who wants to take Ash's place. This trainer might use dark magic or some underhanded tactics to make Ash's Pokemon abandon him so that he can swoop in and claim them for his own.
Perhaps the main antagonist is actually an old enemy who manipulates Naruto's team into abandoning him. This enemy could be using mind - control or false information to drive a wedge between Naruto and his team. They do this to weaken Naruto, knowing that his strength comes from his relationships.
Perhaps it could be another entity related to Hagoromo. If Naruto abandons Hagoromo, there might be a counterpart or a follower of Hagoromo who sees Naruto as a threat or a traitor. This person could then become the main antagonist, trying to either bring Naruto back to Hagoromo's side or simply eliminate him.