A villain with an ice - based quirk could be a great antagonist. The contrast between Izuku's fiery Phoenix quirk and the ice - based powers would create interesting battle dynamics. The villain could be constantly trying to freeze Izuku and put out his phoenix flames.
How about a villain with a time - stopping quirk? This would be a huge challenge for Izuku. When the time is stopped, his Phoenix quirk may not be able to function as normal. He would have to find a way to break free from the time - stopped state or find a way to use his quirk in a different way that doesn't rely on normal time flow.
A shadow - manipulating villain would also work well. This villain could use shadows to try and suffocate Izuku's Phoenix form or even try to corrupt the phoenix energy. They might be able to hide in the shadows and launch surprise attacks, making it difficult for Izuku to counter.
His classmates could be his allies. They might be intrigued by his Pokemon - quirk and offer to help him train or use it better. For instance, Ochaco could use her zero - gravity quirk to assist Izuku in some Pokemon - quirk - related training exercises.
His relationship with his mother could become more complex. She might be worried about his new nature and try to protect him more. With his friends, like Bakugo, they might initially be scared or distrustful when they find out about his quirk.
A possible plot could be centered around Izuku's struggle to control his Phoenix quirk. Since it's such a powerful and volatile quirk, he often loses control. This causes problems not only for him but also for his friends and the people around him. He then has to seek out an old, reclusive hero who once had a similar quirk to learn how to master it.
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.
Bakugo is often a key character. In many fanfictions, Bakugo's reaction to Izuku's evolving quirk can range from envy to begrudging respect. Their relationship is always a central focus, with Bakugo either trying to outdo Izuku or having to come to terms with Izuku's newfound power.
Bakugo is often paired with Izuku. Their complex relationship from the original series can be further explored in fanfiction with Izuku's growth quirk. All Might is also a common character paired with Izuku. He could play a role in guiding Izuku to control and develop his growth quirk. Ochaco is another one. She might be involved in stories where Izuku's growth quirk affects his relationships, especially romantic ones.
Bakugo is often paired with Izuku. Their relationship is complex in the original series, and in fanfiction with Izuku's time quirk, it could add more depth. Bakugo might be jealous of Izuku's new power at first but then come to respect it as they face challenges together.
Bakugo could also be popular. In a lot of fanfictions, Bakugo's fiery personality clashes with Izuku's more stealthy ninja - like nature. Their interactions can create a lot of drama and interesting storylines.
In many fanfictions, Ochaco Uraraka might be one of those in 1A who knows about Izuku's quirk. She is his close friend and often involved in his life and battles, so it's likely she would be aware of his quirk's details in fan - created stories.