Who are the main antagonists they might face in the 'Luke and Rey go back in time' fanfiction?

Well, they might prevent some great tragedies in the Star Wars universe. For example, they could stop Anakin from turning to the Dark Side. This would completely change the course of history in the galaxy.

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.

Often, Palpatine can still be a main antagonist even in time travel fanfiction. If Luke and Leia travel back in time, he might sense their presence and try to stop them from changing things that would undermine his power. Another could be Darth Vader if they travel to a time when he was still firmly on the dark side. He would be a powerful foe for them to face.

They might face the challenge of not being recognized by their past selves or other characters. Also, they could accidentally change things in a way that creates new and more dangerous villains. Another challenge could be dealing with the technology and power levels of the past, which are much lower than what they are used to.

One of the main antagonists could be the Titans that were banished to Tartarus. They are powerful and hold grudges against the demigods. For example, Kronos' influence might still be felt in Tartarus, and his minions could try to stop Percy and Piper.

The Emperor could still be a major antagonist. Even though Anakin turned on him in the end, his influence might still be felt. He could send his agents to try and find baby Luke to eliminate any potential threats to his power.

Perhaps Orochimaru, if he somehow discovers Ino's time - traveling. He has always been interested in power and forbidden jutsu. He might try to use Ino's ability for his own gain, and if she resists, he would become an antagonist. He could also try to stop her from changing things that he wants to keep as they are for his own evil purposes.

In some cases, it could be other time - traveling vampires or supernatural beings who have their own agendas. They might not want Bella to interfere with the past as it could disrupt their own plans or power bases. These antagonists could be more shadowy figures, working behind the scenes to thwart Bella's efforts.

Team Rocket could still be antagonists. Even if Ash goes back in time, they might be up to their old tricks of trying to steal Pokémon. Only this time, Ash has the advantage of knowing their future plans and can thwart them more easily.

Another possibility is a group or organization that has different ideals. If Thalia and Luke are part of a group that values something different from them, that group could oppose their decision to have a child and become the main antagonists, trying to stop the pregnancy or take the baby away once it's born.