Well, Bakugou might struggle to control One for All at first. It's a powerful quirk and he has his own explosive temper. He could accidentally cause a lot of destruction while trying to master it.
It's possible that Bakugou, with One for All, would start to develop new combat techniques. He'd combine his natural aggression and the new power. He might also face new enemies who are attracted to the power of One for All that he now possesses. This could put him in some really tough situations where he has to learn to use the quirk effectively and quickly to survive.
He could start to notice things from a different perspective. As a girl, Bakugou might become more aware of the way others perceive her appearance. She might also start to develop different interests, like taking more interest in fashion or something that she previously didn't care about. This could lead to some really interesting character development, especially if she still tries to hold on to her tough - guy (or now tough - girl) attitude.
Midoriya is often a common character. Since he has a complex relationship with Bakugou, his reaction to Bakugou's expulsion can be an important part of the story. All Might might also be included as he could be a mentor figure who tries to guide Bakugou, even after his expulsion. And Bakugou's other classmates like Kirishima would likely be there too, as they are his friends and would be affected by his leaving.
He might become more responsible. Since One for All is such a significant power, he'd have to step up. He couldn't just be as reckless as he used to be.
One possible plot could be that Bakugou is in the middle of a battle with villains. He's being his usual brash self, charging ahead. Suddenly, a sniper from the villains' side takes aim and shoots him. His friends then have to rush to his aid and figure out how to get him medical help while still fending off the villains.
He might lose his own quirk temporarily. In some fanfictions, a quirk hit can disrupt a character's own power system.
There's also a possibility that it's an agent of a secret organization. This organization might be aiming to disrupt the hero society, and they see Bakugou as a key figure to target. So they send one of their best shooters to take him down.
One possible plotline could be Bakugou's journey to redeem himself after the expulsion. He might have to face his own flaws and work hard to prove that he can change. Another could be how his friends react to his expulsion, some might be shocked while others might try to help him get back in. Maybe there's a plotline where he discovers a new power or ability during his time away from school that makes him even stronger when he eventually returns.
It might be a tale where Bakugou's arrogance and bad behavior lead to a downfall. Could involve being defeated by a rival or losing something important.
If it's a fanfiction about Class 1A meeting Bakugou's boyfriend, there could be a lot of comical moments. Maybe Mineta would try to be inappropriate and get scolded by Bakugou. The more responsible students like Iida might give Bakugou relationship advice. His boyfriend could be from another class or even another school. If he's from another school, Class 1A would be curious about the differences in their hero training. And Bakugou would have to balance his relationship with his training and his place in Class 1A.
Bakugou's pride would likely be affected. As a girl, he might feel a bit more self - conscious about it. He could be more defensive when people question his abilities. At the same time, he might also learn to use his new form to his advantage in some situations, like when trying to deceive opponents in battle. His personality would be a mix of his old self and new adaptations due to the change.