Maybe a new villain that is created specifically for this fanfiction. This villain could be a former student who was wronged by the hero society and now wants revenge. They would target both the real Class 1A and the 'Villain Class 1A' as symbols of the hero system they despise.
It could be All For One. He might see the 'Villain Class 1A' as a useful tool to further his own evil plans. He could manipulate them into doing his bidding, which would put them in direct conflict with the heroes, including Class 1A.
Perhaps an all - powerful villain from another dimension invades. This villain has the ability to control the minds of those with quirks and uses them to fight against the remaining heroes. He wants to take over the 'My Hero Academia' world and remake it in his own image. His powers are so strong that it takes all of the heroes' combined efforts just to try and figure out a way to stop him.
A group of villains who specialize in causing chaos during disasters could also be the main antagonists. They would constantly try to undermine Backdraft's efforts to keep the city safe during fires and other emergencies.
One idea could be that the 'Villain Class 1A' has to team up with the real Class 1A to fight a greater threat. Maybe a new super - villain emerges who is too powerful for either group alone. This would lead to some really interesting character dynamics as they have to put aside their differences.
I'm not sure exactly what you're asking. If you mean whether Class 1 - A in 'My Hero Academia' could be depicted as watching fanfiction in fan - made stories, it's possible. Fanfiction often takes creative liberties with the existing characters and their actions.
Perhaps Class A would be quite intrigued when watching 'My Hero Academia' fanfiction. They could see how fans outside their universe view their powers, relationships, and adventures. It might even inspire them in some ways.
It could be a powerful villain who sees Naruto as a threat to his plans in the My Hero Academia world. Maybe a villain who wants to use Naruto's unique abilities for his own evil purposes and when Naruto refuses, becomes his enemy.
It could be a rogue scientist. They might be jealous of the natural quirks that people are born with and decide to steal them to create artificial super - beings. They would be highly intelligent and use their scientific knowledge to develop devices or techniques to steal quirks.
A possible main antagonist could be a scientist - turned - villain. This character could have created the situation where Deku needs oxygen in the first place. He might be obsessed with creating the 'perfect' hero and when Deku doesn't fit his mold, he decides to try and destroy him. The villain could use his scientific knowledge to create various obstacles for Deku related to his oxygen - dependent state.
It could be the scientists or villains who turned Deku into a Noumu. They might want to use him for their evil plans, like taking over the hero society.
Dabi could also be a main villain in such a fanfiction. His mysterious past and his powerful fire - based quirk would make for an exciting addition to UA. He could go to UA to spy on the heroes - in - training, but end up getting involved in their lives more than he expected. His cynical view of the hero society would clash with the positive environment at UA, and he might even start to question his own motives while there.