Who could be the main antagonists in 'izuku becomes a girl fanfiction'?

It could be the traditional God of War villains like the gods who oppose Izuku. Maybe Ares, if he's still around in the fanfiction's version of the God of War world, would see Izuku as a threat and try to stop him.

Some of the teachers at U.A. might also be antagonists. They could be secretly working for an organization that wants to control Izuku's powers for their own evil purposes. They would pretend to be helpful while actually setting traps and spreading misinformation about him.

It could be other villains who are jealous of Izuku's powerful dragon quirk. They might see his quirk as a threat to their own plans for domination or chaos.

The League of Villains would be obvious antagonists. They'd see Izuku with the All for One quirk as a threat or a potential recruit. Shigaraki, in particular, might be envious and want to take the quirk for himself.

The Joker could be a great villain. Imagine if the Joker - like character emerged in the My Hero Academia world. Izuku, with his new Batman - inspired skills, would have to use his wits to outsmart this chaotic and unpredictable foe.

There could be an old dragon that has been in exile for a long time. This dragon might see Hiccup as a threat to its plan of taking over the dragon kingdom. So it tries to stop Hiccup from fully becoming a dragon or tries to use his new form for its own evil purposes.

Perhaps the very magic that made Harry a god has a sort of negative side - effect. This could manifest as a shadowy entity within Harry that tries to take over his mind and use his powers for evil. So, in a way, this internal struggle could be the main antagonist in the story.

One potential main antagonist could be a powerful pirate captain who sees Harry as a threat to his control over the seas. Maybe this captain has some dark magic powers as well.

The Hidden Leaf Village elders could be antagonists. If Naruto turns dark, they might see him as a threat to their power and try to stop him. Their actions against Naruto could further fuel his descent into darkness.

Morgana could be a main antagonist. She has her own desires for power and may see Merlin's rise to kingship as a threat to her plans. So she tries to stop him at every turn, using her dark magic against him.