Who could be the main antagonists in 'Luffy trained by Dragon' fanfiction?

The World Government could still be the main antagonists. Since Luffy is getting stronger under Mihawk's training, they would see him as an even greater threat. They might send their top agents, like the Cipher Pol units, to try and stop Luffy's progress.

Perhaps Dragon would also introduce Luffy to some new allies or inform him about the greater political and power struggles in the world of One Piece. This would give Luffy a broader perspective and help him understand the significance of his actions. He might learn about the true nature of the World Government and how to better fight against it, not just for the sake of his crew and friends, but for the freedom of the entire world.

There could be an ancient evil force that awakens because of Luffy's new powers. This force was once sealed away but now wants to destroy Luffy and everything he stands for, seeing him as a disruption to the balance it once knew.

In this fanfiction, there might be a group of wizards who oppose the idea of mixing magic with the skills taught by Hephaestus. They could be the antagonists as they try to prevent Harry from using his new - found skills. They might believe that this new form of magic is dangerous or against the traditional ways of the wizarding world. They could form an organization to oppose Harry and try to disrupt his training and any plans he has to use his skills for good.

Well, in this fanfiction, the Akatsuki could be the main antagonists. They would view Naruto's godlike powers as a major threat to their goals. Since Naruto has been trained by Shendu, his abilities would be unpredictable and extremely powerful. They might band together to try and take Naruto down. Additionally, there could be some ancient demons or spirits that are awakened by Naruto's new powers and they see him as an intruder in their realm, so they become antagonists as well. They would use their own dark magic and powers to oppose Naruto.

Perhaps some traditionalist wizards in the Ministry of Magic. They might view Harry's training by snakes as a form of dark magic practice, even if it's not. So they become the antagonists, trying to arrest Harry or stop his training in some way.

The Yonko would definitely be major antagonists. Since Luffy is in the New World, the likes of Kaido or Big Mom would be natural choices. Their vast power and influence would pose a great threat to Luffy and his crew.

The Marines could be antagonists. They might see the baby as a threat or something that needs to be taken away from Luffy and Nami's crew. Maybe they think the baby has some connection to a dangerous pirate or revolutionary. The Marines would try to capture the baby and arrest Luffy and Nami for having it.

The Akatsuki could still be the main antagonists. Even with Naruto's training by the Kyuubi, they would be after the tailed beasts. Their goals of collecting all the tailed beasts would put them in direct conflict with Naruto. And they have some really powerful members like Pain and Itachi.

Often, the Marines can be main antagonists. They see pirates as a threat, and with Ace and Luffy being pirates, they would be constantly on the Marines' radar. Marines like Akainu are especially dangerous, as his extreme sense of justice could lead to direct confrontations with the brothers.